[v3,1/6] Add an "info pg" command that prints the current page tables

The new "info pg" monitor command prints the current page table,
including virtual address ranges, flag bits, and snippets of physical
page numbers.  Completely filled regions of the page table with
compatible flags are "folded", with the result that the complete
output for a freshly booted x86-64 Linux VM can fit in a single
terminal window.  The output looks like this:

VPN range             Entry         Flags            Physical page
[7f0000000-7f0000000] PML4[0fe]     ---DA--UWP
  [7f28c0000-7f28fffff]  PDP[0a3]     ---DA--UWP
    [7f28c4600-7f28c47ff]  PDE[023]     ---DA--UWP
      [7f28c4655-7f28c4656]  PTE[055-056] X--D---U-P 0000007f14-0000007f15
      [7f28c465b-7f28c465b]  PTE[05b]     ----A--U-P 0000001cfc
...
[ff8000000-ff8000000] PML4[1ff]     ---DA--UWP
  [ffff80000-ffffbffff]  PDP[1fe]     ---DA---WP
    [ffff81000-ffff81dff]  PDE[008-00e] -GSDA---WP 0000001000-0000001dff
  [ffffc0000-fffffffff]  PDP[1ff]     ---DA--UWP
    [ffffff400-ffffff5ff]  PDE[1fa]     ---DA--UWP
      [ffffff5fb-ffffff5fc]  PTE[1fb-1fc] XG-DACT-WP 00000fec00 00000fee00
    [ffffff600-ffffff7ff]  PDE[1fb]     ---DA--UWP
      [ffffff600-ffffff600]  PTE[000]     -G-DA--U-P 0000001467

This draws heavy inspiration from Austin Clements' original patch.

This also adds a generic page table walker, which other monitor
and execution commands will be migrated to in subsequent patches.

Signed-off-by: Don Porter <porter@cs.unc.edu>
---
 hmp-commands-info.hx              |  13 ++
 hw/core/cpu-sysemu.c              | 140 ++++++++++++
 include/hw/core/cpu.h             |  34 ++-
 include/hw/core/sysemu-cpu-ops.h  | 156 +++++++++++++
 include/monitor/hmp-target.h      |   1 +
 monitor/hmp-cmds-target.c         | 198 +++++++++++++++++
 target/i386/arch_memory_mapping.c | 351 +++++++++++++++++++++++++++++-
 target/i386/cpu.c                 |  11 +
 target/i386/cpu.h                 |  15 ++
 target/i386/monitor.c             | 165 ++++++++++++++
 10 files changed, 1082 insertions(+), 2 deletions(-)

On 6/6/24 16:02, Don Porter wrote:
> The new "info pg" monitor command prints the current page table,
> including virtual address ranges, flag bits, and snippets of physical
> page numbers.  Completely filled regions of the page table with
> compatible flags are "folded", with the result that the complete
> output for a freshly booted x86-64 Linux VM can fit in a single
> terminal window.  The output looks like this:
> 
> VPN range             Entry         Flags            Physical page
> [7f0000000-7f0000000] PML4[0fe]     ---DA--UWP
>    [7f28c0000-7f28fffff]  PDP[0a3]     ---DA--UWP
>      [7f28c4600-7f28c47ff]  PDE[023]     ---DA--UWP
>        [7f28c4655-7f28c4656]  PTE[055-056] X--D---U-P 0000007f14-0000007f15
>        [7f28c465b-7f28c465b]  PTE[05b]     ----A--U-P 0000001cfc
> ...
> [ff8000000-ff8000000] PML4[1ff]     ---DA--UWP
>    [ffff80000-ffffbffff]  PDP[1fe]     ---DA---WP
>      [ffff81000-ffff81dff]  PDE[008-00e] -GSDA---WP 0000001000-0000001dff
>    [ffffc0000-fffffffff]  PDP[1ff]     ---DA--UWP
>      [ffffff400-ffffff5ff]  PDE[1fa]     ---DA--UWP
>        [ffffff5fb-ffffff5fc]  PTE[1fb-1fc] XG-DACT-WP 00000fec00 00000fee00
>      [ffffff600-ffffff7ff]  PDE[1fb]     ---DA--UWP
>        [ffffff600-ffffff600]  PTE[000]     -G-DA--U-P 0000001467
> 
> This draws heavy inspiration from Austin Clements' original patch.
> 
> This also adds a generic page table walker, which other monitor
> and execution commands will be migrated to in subsequent patches.
> 
> Signed-off-by: Don Porter <porter@cs.unc.edu>
> ---
>   hmp-commands-info.hx              |  13 ++
>   hw/core/cpu-sysemu.c              | 140 ++++++++++++
>   include/hw/core/cpu.h             |  34 ++-
>   include/hw/core/sysemu-cpu-ops.h  | 156 +++++++++++++
>   include/monitor/hmp-target.h      |   1 +
>   monitor/hmp-cmds-target.c         | 198 +++++++++++++++++
>   target/i386/arch_memory_mapping.c | 351 +++++++++++++++++++++++++++++-
>   target/i386/cpu.c                 |  11 +
>   target/i386/cpu.h                 |  15 ++
>   target/i386/monitor.c             | 165 ++++++++++++++
>   10 files changed, 1082 insertions(+), 2 deletions(-)
> 
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 20a9835ea8..a873841920 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -242,6 +242,19 @@ SRST
>       Show memory tree.
>   ERST
>   
> +    {
> +        .name       = "pg",
> +        .args_type  = "",
> +        .params     = "",
> +        .help       = "show the page table",
> +        .cmd        = hmp_info_pg,
> +    },
> +
> +SRST
> +  ``info pg``
> +    Show the active page table.
> +ERST
> +
>   #if defined(CONFIG_TCG)
>       {
>           .name       = "jit",
> diff --git a/hw/core/cpu-sysemu.c b/hw/core/cpu-sysemu.c
> index 2a9a2a4eb5..fd936fa90c 100644
> --- a/hw/core/cpu-sysemu.c
> +++ b/hw/core/cpu-sysemu.c
> @@ -142,3 +142,143 @@ GuestPanicInformation *cpu_get_crash_info(CPUState *cpu)
>       }
>       return res;
>   }
> +
> +/**
> + * _for_each_pte - recursive helper function
> + *
> + * @cs - CPU state
> + * @fn(cs, data, pte, vaddr, height) - User-provided function to call on each
> + *                                     pte.
> + *   * @cs - pass through cs
> + *   * @data - user-provided, opaque pointer
> + *   * @pte - current pte
> + *   * @vaddr_in - virtual address translated by pte
> + *   * @height - height in the tree of pte
> + * @data - user-provided, opaque pointer, passed to fn()
> + * @visit_interior_nodes - if true, call fn() on page table entries in
> + *                         interior nodes.  If false, only call fn() on page
> + *                         table entries in leaves.
> + * @visit_not_present - if true, call fn() on entries that are not present.
> + *                         if false, visit only present entries.
> + * @node - The physical address of the current page table radix tree node
> + * @vaddr_in - The virtual address bits translated in walking the page
> + *          table to node
> + * @height - The height of node in the radix tree
> + *
> + * height starts at the max and counts down.
> + * In a 4 level x86 page table, pml4e is level 4, pdpe is level 3,
> + *  pde is level 2, and pte is level 1
> + *
> + * Returns true on success, false on error.
> + */
> +static bool
> +_for_each_pte(CPUState *cs,

Please avoid '_' prefix.

> +              int (*fn)(CPUState *cs, void *data, PTE_t *pte,
> +                        vaddr vaddr_in, int height, int offset),
> +              void *data, bool visit_interior_nodes,
> +              bool visit_not_present, hwaddr node,
> +              vaddr vaddr_in, int height)
> +{
> +    int ptes_per_node;
> +    int i;
> +
> +    assert(height > 0);
> +
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +
> +    if ((!cc->sysemu_ops->page_table_entries_per_node)
> +        || (!cc->sysemu_ops->get_pte)
> +        || (!cc->sysemu_ops->pte_present)
> +        || (!cc->sysemu_ops->pte_leaf)
> +        || (!cc->sysemu_ops->pte_child)) {
> +        return false;

Since this function has local scope, it shouldn't be called with
any of these unset. If you are unsure, we can assert() on them.

> +    }
> +
> +    ptes_per_node = cc->sysemu_ops->page_table_entries_per_node(cs, height);
> +
> +    for (i = 0; i < ptes_per_node; i++) {
> +        PTE_t pt_entry;
> +        vaddr vaddr_i;
> +        bool pte_present;
> +
> +        cc->sysemu_ops->get_pte(cs, node, i, height, &pt_entry, vaddr_in,
> +                                &vaddr_i, NULL);
> +        pte_present = cc->sysemu_ops->pte_present(cs, &pt_entry);
> +
> +        if (pte_present || visit_not_present) {
> +            if ((!pte_present) || cc->sysemu_ops->pte_leaf(cs, height,
> +                                                           &pt_entry)) {
> +                if (fn(cs, data, &pt_entry, vaddr_i, height, i)) {
> +                    /* Error */
> +                    return false;
> +                }
> +            } else { /* Non-leaf */
> +                if (visit_interior_nodes) {
> +                    if (fn(cs, data, &pt_entry, vaddr_i, height, i)) {
> +                        /* Error */
> +                        return false;
> +                    }
> +                }
> +                hwaddr child = cc->sysemu_ops->pte_child(cs, &pt_entry, height);
> +                assert(height > 1);
> +                if (!_for_each_pte(cs, fn, data, visit_interior_nodes,
> +                                   visit_not_present, child, vaddr_i,
> +                                   height - 1)) {
> +                    return false;
> +                }
> +            }
> +        }
> +    }
> +
> +    return true;
> +}
> +
> +/**
> + * for_each_pte - iterate over a page table, and
> + *                call fn on each entry
> + *
> + * @cs - CPU state
> + * @fn(cs, data, pte, vaddr, height) - User-provided function to call on each
> + *                                     pte.
> + *   * @cs - pass through cs
> + *   * @data - user-provided, opaque pointer
> + *   * @pte - current pte
> + *   * @vaddr - virtual address translated by pte
> + *   * @height - height in the tree of pte
> + * @data - opaque pointer; passed through to fn
> + * @visit_interior_nodes - if true, call fn() on interior entries in
> + *                         page table; if false, visit only leaf entries.
> + * @visit_not_present - if true, call fn() on entries that are not present.
> + *                         if false, visit only present entries.
> + *
> + * Returns true on success, false on error.
> + *
> + */
> +bool for_each_pte(CPUState *cs,
> +                  int (*fn)(CPUState *cs, void *data, PTE_t *pte,
> +                            vaddr vaddr, int height, int offset),
> +                  void *data, bool visit_interior_nodes,
> +                  bool visit_not_present)
> +{
> +    int height;
> +    vaddr vaddr = 0;
> +    hwaddr root;
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +
> +    if (!cpu_paging_enabled(cs)) {
> +        /* paging is disabled */
> +        return true;
> +    }
> +
> +    if (!cc->sysemu_ops->page_table_root) {
> +        return false;
> +    }
> +
> +    root = cc->sysemu_ops->page_table_root(cs, &height);
> +
> +    assert(height > 1);
> +
> +    /* Recursively call a helper to walk the page table */
> +    return _for_each_pte(cs, fn, data, visit_interior_nodes, visit_not_present,
> +                         root, vaddr, height);
> +}
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index a2c8536943..00d7162795 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -671,9 +671,41 @@ int cpu_write_elf32_qemunote(WriteCoreDumpFunction f, CPUState *cpu,
>    * Caller is responsible for freeing the data.
>    */
>   GuestPanicInformation *cpu_get_crash_info(CPUState *cpu);
> -
>   #endif /* !CONFIG_USER_ONLY */
>   
> +/* Intended to become a generic PTE type */
> +typedef union PTE {
> +    uint64_t pte64_t;
> +    uint32_t pte32_t;
> +} PTE_t;
> +
> +/**
> + * for_each_pte - iterate over a page table, and
> + *                call fn on each entry
> + *
> + * @cs - CPU state
> + * @fn(cs, data, pte, vaddr, height) - User-provided function to call on each
> + *                                     pte.
> + *   * @cs - pass through cs
> + *   * @data - user-provided, opaque pointer
> + *   * @pte - current pte
> + *   * @vaddr - virtual address translated by pte
> + *   * @height - height in the tree of pte
> + * @data - opaque pointer; passed through to fn
> + * @visit_interior_nodes - if true, call fn() on interior entries in
> + *                         page table; if false, visit only leaf entries.
> + * @visit_not_present - if true, call fn() on entries that are not present.
> + *                         if false, visit only present entries.
> + *
> + * Returns true on success, false on error.
> + *
> + */
> +bool for_each_pte(CPUState *cs,
> +                  int (*fn)(CPUState *cs, void *data, PTE_t *pte, vaddr vaddr,
> +                            int height, int offset), void *data,
> +                  bool visit_interior_nodes, bool visit_not_present);
> +
> +
>   /**
>    * CPUDumpFlags:
>    * @CPU_DUMP_CODE:
> diff --git a/include/hw/core/sysemu-cpu-ops.h b/include/hw/core/sysemu-cpu-ops.h
> index 24d003fe04..eb16a1c3e2 100644
> --- a/include/hw/core/sysemu-cpu-ops.h
> +++ b/include/hw/core/sysemu-cpu-ops.h
> @@ -12,6 +12,39 @@
>   
>   #include "hw/core/cpu.h"
>   
> +/* Maximum supported page table height - currently x86 at 5 */
> +#define MAX_HEIGHT 5
> +
> +/*
> + * struct mem_print_state: Used by monitor in walking page tables.
> + */
> +struct mem_print_state {
> +    Monitor *mon;

I'd rather keep the monitor out of this state.

> +    CPUArchState *env;
> +    int vaw, paw; /* VA and PA width in characters */
> +    int max_height;
> +    bool (*flusher)(CPUState *cs, struct mem_print_state *state);
> +    bool flush_interior; /* If false, only call flusher() on leaves */
> +    bool require_physical_contiguity;
> +    /*
> +     * The height at which we started accumulating ranges, i.e., the
> +     * next height we need to print once we hit the end of a
> +     * contiguous range.
> +     */
> +    int start_height;
> +    /*
> +     * For compressing contiguous ranges, track the
> +     * start and end of the range
> +     */
> +    hwaddr vstart[MAX_HEIGHT + 1]; /* Starting virt. addr. of open pte range */
> +    hwaddr vend[MAX_HEIGHT + 1]; /* Ending virtual address of open pte range */
> +    hwaddr pstart; /* Starting physical address of open pte range */
> +    hwaddr pend; /* Ending physical address of open pte range */
> +    int64_t ent[MAX_HEIGHT + 1]; /* PTE contents on current root->leaf path */
> +    int offset[MAX_HEIGHT + 1]; /* PTE range starting offsets */
> +    int last_offset[MAX_HEIGHT + 1]; /* PTE range ending offsets */
> +};
> +
>   /*
>    * struct SysemuCPUOps: System operations specific to a CPU class
>    */
> @@ -87,6 +120,129 @@ typedef struct SysemuCPUOps {
>        */
>       const VMStateDescription *legacy_vmsd;
>   
> +    /**
> +     * page_table_root - Given a CPUState, return the physical address
> +     *                    of the current page table root, as well as
> +     *                    write the height of the tree into *height.
> +     *
> +     * @cs - CPU state
> +
> +     * @height - a pointer to an integer, to store the page table tree
> +     *           height
> +     *
> +     * Returns a hardware address on success.  Should not fail (i.e.,
> +     * caller is responsible to ensure that a page table is actually
> +     * present).
> +     */
> +    hwaddr (*page_table_root)(CPUState *cs, int *height);
> +
> +    /**
> +     * page_table_entries_per_node - Return the number of entries in a
> +     *                                   page table node for the CPU
> +     *                                   at a given height.
> +     *
> +     * @cs - CPU state
> +     * @height - height of the page table tree to query, where the leaves
> +     *          are 1.
> +     *
> +     * Returns a value greater than zero on success, -1 on error.
> +     */
> +    int (*page_table_entries_per_node)(CPUState *cs, int height);
> +
> +    /**
> +     * get_pte - Copy the contents of the page table entry at node[i]
> +     *           into pt_entry.  Optionally, add the relevant bits to
> +     *           the virtual address in vaddr_pte.
> +     *
> +     * @cs - CPU state
> +     * @node - physical address of the current page table node
> +     * @i - index (in page table entries, not bytes) of the page table
> +     *      entry, within node
> +     * @height - height of node within the tree (leaves are 1, not 0)
> +     * @pt_entry - Pointer to a PTE_t, stores the contents of the page
> +     *             table entry
> +     * @vaddr_parent - The virtual address bits already translated in
> +     *                 walking the page table to node.  Optional: only
> +     *                 used if vaddr_pte is set.
> +     * @vaddr_pte - Optional pointer to a variable storing the virtual
> +     *              address bits translated by node[i].
> +     * @pte_paddr - Pointer to the physical address of the PTE within node.
> +     *              Optional parameter.
> +     */
> +
> +    void (*get_pte)(CPUState *cs, hwaddr node, int i, int height,
> +                    PTE_t *pt_entry, vaddr vaddr_parent, vaddr *vaddr_pte,
> +                    hwaddr *pte_paddr);
> +
> +    /**
> +     * pte_present - Return true if the pte is marked 'present'
> +     */
> +    bool (*pte_present)(CPUState *cs, PTE_t *pte);
> +
> +    /**
> +     * pte_leaf - Return true if the pte is a page table leaf, false
> +     *                if the pte points to another node in the radix
> +     *                tree.
> +     */
> +    bool (*pte_leaf)(CPUState *cs, int height, PTE_t *pte);
> +
> +    /**
> +     * pte_child - Returns the physical address of a radix tree node
> +     *                 pointed to by pte.
> +     *
> +     * @cs - CPU state
> +     * @pte - The page table entry
> +     * @height - The height in the tree of pte
> +     *
> +     * Returns the physical address stored in pte on success, -1 on
> +     * error.
> +     */
> +    hwaddr (*pte_child)(CPUState *cs, PTE_t *pte, int height);
> +
> +    /**
> +     * pte_leaf_page_size - Return the page size of a leaf entry,
> +     *                          given the height and CPU state
> +     *
> +     * @cs - CPU state
> +     * @height - height of the page table tree to query, where the leaves
> +     *          are 1.
> +     *
> +     * Returns a value greater than zero on success, -1 on error.
> +     */
> +    uint64_t (*pte_leaf_page_size)(CPUState *cs, int height);
> +
> +    /**
> +     * pte_flags - Return the flag bits of the page table entry.
> +     *
> +     * @pte - the contents of the PTE, not the address.
> +     *
> +     * Returns pte with the non-flag bits masked out.
> +     */
> +    uint64_t (*pte_flags)(uint64_t pte);
> +
> +    /**
> +     * @mon_init_page_table_iterator: Callback to configure a page table
> +     * iterator for use by a monitor function.
> +     * Returns true on success, false if not supported (e.g., no paging disabled
> +     * or not implemented on this CPU).
> +     */
> +    bool (*mon_init_page_table_iterator)(Monitor *mon,
> +                                         struct mem_print_state *state);

Here too, I'm reluctant to wire the monitor to this API.

If we want text, we should use HumanReadableText.

> +    /**
> +     * @mon_info_pg_print_header: Prints the header line for 'info pg'.
> +     */
> +    void (*mon_info_pg_print_header)(Monitor *mon,
> +                                     struct mem_print_state *state);
> +
> +    /**
> +     * @flush_page_table_iterator_state: Prints the last entry,
> +     * if one is present.  Useful for iterators that aggregate information
> +     * across page table entries.
> +     */
> +    bool (*mon_flush_page_print_state)(CPUState *cs,
> +                                       struct mem_print_state *state);
> +
>   } SysemuCPUOps;
>   
>   #endif /* SYSEMU_CPU_OPS_H */
> diff --git a/include/monitor/hmp-target.h b/include/monitor/hmp-target.h
> index b679aaebbf..9af72ea58d 100644
> --- a/include/monitor/hmp-target.h
> +++ b/include/monitor/hmp-target.h
> @@ -50,6 +50,7 @@ CPUState *mon_get_cpu(Monitor *mon);
>   void hmp_info_mem(Monitor *mon, const QDict *qdict);
>   void hmp_info_tlb(Monitor *mon, const QDict *qdict);
>   void hmp_mce(Monitor *mon, const QDict *qdict);
> +void hmp_info_pg(Monitor *mon, const QDict *qdict);
>   void hmp_info_local_apic(Monitor *mon, const QDict *qdict);
>   void hmp_info_sev(Monitor *mon, const QDict *qdict);
>   void hmp_info_sgx(Monitor *mon, const QDict *qdict);
> diff --git a/monitor/hmp-cmds-target.c b/monitor/hmp-cmds-target.c
> index ff01cf9d8d..60a8bd0c37 100644
> --- a/monitor/hmp-cmds-target.c
> +++ b/monitor/hmp-cmds-target.c
> @@ -31,6 +31,7 @@
>   #include "qapi/error.h"
>   #include "qapi/qmp/qdict.h"
>   #include "sysemu/hw_accel.h"
> +#include "hw/core/sysemu-cpu-ops.h"
>   
>   /* Set the current CPU defined by the user. Callers must hold BQL. */
>   int monitor_set_cpu(Monitor *mon, int cpu_index)
> @@ -120,6 +121,203 @@ void hmp_info_registers(Monitor *mon, const QDict *qdict)
>       }
>   }
>   
> +/* Assume only called on present entries */
> +static
> +int compressing_iterator(CPUState *cs, void *data, PTE_t *pte,
> +                         vaddr vaddr_in, int height, int offset)
> +{
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +    struct mem_print_state *state = (struct mem_print_state *) data;
> +    hwaddr paddr = cc->sysemu_ops->pte_child(cs, pte, height);
> +    target_ulong size = cc->sysemu_ops->pte_leaf_page_size(cs, height);
> +    bool start_new_run = false, flush = false;
> +    bool is_leaf = cc->sysemu_ops->pte_leaf(cs, height, pte);
> +
> +    int entries_per_node = cc->sysemu_ops->page_table_entries_per_node(cs,
> +                                                                       height);
> +
> +    /* Prot of current pte */
> +    int prot = cc->sysemu_ops->pte_flags(pte->pte64_t);
> +
> +    /* If there is a prior run, first try to extend it. */
> +    if (state->start_height != 0) {
> +
> +        /*
> +         * If we aren't flushing interior nodes, raise the start height.
> +         * We don't need to detect non-compressible interior nodes.
> +         */
> +        if ((!state->flush_interior) && state->start_height < height) {
> +            state->start_height = height;
> +            state->vstart[height] = vaddr_in;
> +            state->vend[height] = vaddr_in;
> +            state->ent[height] = pte->pte64_t;
> +            if (offset == 0) {
> +                state->last_offset[height] = entries_per_node - 1;
> +            } else {
> +                state->last_offset[height] = offset - 1;
> +            }
> +        }
> +
> +        /* Detect when we are walking down the "left edge" of a range */
> +        if (state->vstart[height] == -1
> +            && (height + 1) <= state->start_height
> +            && state->vstart[height + 1] == vaddr_in) {
> +
> +            state->vstart[height] = vaddr_in;
> +            state->vend[height] = vaddr_in;
> +            state->ent[height] = pte->pte64_t;
> +            state->offset[height] = offset;
> +            state->last_offset[height] = offset;
> +
> +            if (is_leaf) {
> +                state->pstart = paddr;
> +                state->pend = paddr;
> +            }
> +
> +            /* Detect contiguous entries at same level */
> +        } else if ((state->vstart[height] != -1)
> +                   && (state->start_height >= height)
> +                   && cc->sysemu_ops->pte_flags(state->ent[height]) == prot
> +                   && (((state->last_offset[height] + 1) % entries_per_node)
> +                       == offset)
> +                   && ((!is_leaf)
> +                       || (!state->require_physical_contiguity)
> +                       || (state->pend + size == paddr))) {
> +
> +
> +            /*
> +             * If there are entries at the levels below, make sure we
> +             * completed them.  We only compress interior nodes
> +             * without holes in the mappings.
> +             */
> +            if (height != 1) {
> +                for (int i = height - 1; i >= 1; i--) {
> +                    int entries = cc->sysemu_ops->page_table_entries_per_node(
> +                        cs, i);
> +
> +                    /* Stop if we hit large pages before level 1 */
> +                    if (state->vstart[i] == -1) {
> +                        break;
> +                    }
> +
> +                    if ((state->last_offset[i] + 1) != entries) {
> +                        flush = true;
> +                        start_new_run = true;
> +                        break;
> +                    }
> +                }
> +            }
> +
> +
> +            if (!flush) {
> +
> +                /* We can compress these entries */
> +                state->ent[height] = pte->pte64_t;
> +                state->vend[height] = vaddr_in;
> +                state->last_offset[height] = offset;
> +
> +                /* Only update the physical range on leaves */
> +                if (is_leaf) {
> +                    state->pend = paddr;
> +                }
> +            }
> +            /* Let PTEs accumulate... */
> +        } else {
> +            flush = true;
> +        }
> +
> +        if (flush) {
> +            /*
> +             * We hit dicontiguous permissions or pages.
> +             * Print the old entries, then start accumulating again
> +             *
> +             * Some clients only want the flusher called on a leaf.
> +             * Check that too.
> +             *
> +             * We can infer whether the accumulated range includes a
> +             * leaf based on whether pstart is -1.
> +             */
> +            if (state->flush_interior || (state->pstart != -1)) {
> +                if (state->flusher(cs, state)) {
> +                    start_new_run = true;
> +                }
> +            } else {
> +                start_new_run = true;
> +            }
> +        }
> +    } else {
> +        start_new_run = true;
> +    }
> +
> +    if (start_new_run) {
> +        /* start a new run with this PTE */
> +        for (int i = state->start_height; i > 0; i--) {
> +            if (state->vstart[i] != -1) {
> +                state->ent[i] = 0;
> +                state->last_offset[i] = 0;
> +                state->vstart[i] = -1;
> +            }
> +        }
> +        state->pstart = -1;
> +        state->vstart[height] = vaddr_in;
> +        state->vend[height] = vaddr_in;
> +        state->ent[height] = pte->pte64_t;
> +        state->offset[height] = offset;
> +        state->last_offset[height] = offset;
> +        if (is_leaf) {
> +            state->pstart = paddr;
> +            state->pend = paddr;
> +        }
> +        state->start_height = height;
> +    }
> +
> +    return 0;
> +}
> +
> +void hmp_info_pg(Monitor *mon, const QDict *qdict)
> +{
> +    struct mem_print_state state;
> +
> +    CPUState *cs = mon_get_cpu(mon);
> +    if (!cs) {
> +        monitor_printf(mon, "Unable to get CPUState.  Internal error\n");
> +        return;
> +    }
> +
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +
> +    if ((!cc->sysemu_ops->pte_child)
> +        || (!cc->sysemu_ops->pte_leaf)
> +        || (!cc->sysemu_ops->pte_leaf_page_size)
> +        || (!cc->sysemu_ops->page_table_entries_per_node)
> +        || (!cc->sysemu_ops->pte_flags)
> +        || (!cc->sysemu_ops->mon_init_page_table_iterator)
> +        || (!cc->sysemu_ops->mon_info_pg_print_header)
> +        || (!cc->sysemu_ops->mon_flush_page_print_state)) {
> +        monitor_printf(mon, "Info pg unsupported on this ISA\n");
> +        return;
> +    }
> +
> +    if (!cc->sysemu_ops->mon_init_page_table_iterator(mon, &state)) {
> +        monitor_printf(mon, "Unable to initialize page table iterator\n");
> +        return;
> +    }
> +
> +    state.flush_interior = true;
> +    state.require_physical_contiguity = true;
> +    state.flusher = cc->sysemu_ops->mon_flush_page_print_state;
> +
> +    cc->sysemu_ops->mon_info_pg_print_header(mon, &state);
> +
> +    /*
> +     * We must visit interior entries to get the hierarchy, but
> +     * can skip not present mappings
> +     */
> +    for_each_pte(cs, &compressing_iterator, &state, true, false);
> +
> +    /* Print last entry, if one present */
> +    cc->sysemu_ops->mon_flush_page_print_state(cs, &state);
> +}
>   static void memory_dump(Monitor *mon, int count, int format, int wsize,
>                           hwaddr addr, int is_physical)
>   {
> diff --git a/target/i386/arch_memory_mapping.c b/target/i386/arch_memory_mapping.c
> index d1ff659128..562a00b5a7 100644
> --- a/target/i386/arch_memory_mapping.c
> +++ b/target/i386/arch_memory_mapping.c
> @@ -15,6 +15,356 @@
>   #include "cpu.h"
>   #include "sysemu/memory_mapping.h"
>   
> +/**
> + ************** code hook implementations for x86 ***********
> + */
> +
> +#define PML4_ADDR_MASK 0xffffffffff000ULL /* selects bits 51:12 */
> +
> +/**
> + * x86_page_table_root - Given a CPUState, return the physical address
> + *                       of the current page table root, as well as
> + *                       write the height of the tree into *height.
> + *
> + * @cs - CPU state
> + * @height - a pointer to an integer, to store the page table tree height
> + *
> + * Returns a hardware address on success.  Should not fail (i.e., caller is
> + * responsible to ensure that a page table is actually present).
> + */
> +hwaddr x86_page_table_root(CPUState *cs, int *height)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    /*
> +     * DEP 5/15/24: Some original page table walking code sets the a20
> +     * mask as a 32 bit integer and checks it on each level of hte
> +     * page table walk; some only checks it against the final result.
> +     * For 64 bits, I think we need to sign extend in the common case
> +     * it is not set (and returns -1), or we will lose bits.
> +     */
> +    int64_t a20_mask;
> +
> +    assert(cpu_paging_enabled(cs));
> +    a20_mask = x86_get_a20_mask(env);
> +
> +    if (env->cr[4] & CR4_PAE_MASK) {
> +#ifdef TARGET_X86_64
> +        if (env->hflags & HF_LMA_MASK) {
> +            if (env->cr[4] & CR4_LA57_MASK) {
> +                *height = 5;
> +            } else {
> +                *height = 4;
> +            }
> +            return (env->cr[3] & PML4_ADDR_MASK) & a20_mask;
> +        } else
> +#endif
> +        {
> +            *height = 3;
> +            return (env->cr[3] & ~0x1f) & a20_mask;
> +        }
> +    } else {
> +        *height = 2;
> +        return (env->cr[3] & ~0xfff) & a20_mask;
> +    }
> +}
> +
> +
> +/**
> + * x86_page_table_entries_per_node - Return the number of entries in a
> + *                                   page table node for the CPU at a
> + *                                   given height.
> + *
> + * @cs - CPU state
> + * @height - height of the page table tree to query, where the leaves
> + *          are 1.
> + *
> + * Returns a value greater than zero on success, -1 on error.
> + */
> +int x86_page_table_entries_per_node(CPUState *cs, int height)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    bool pae_enabled = env->cr[4] & CR4_PAE_MASK;
> +
> +    assert(height < 6);
> +    assert(height > 0);
> +
> +    switch (height) {
> +#ifdef TARGET_X86_64
> +    case 5:
> +        assert(env->cr[4] & CR4_LA57_MASK);
> +    case 4:
> +        assert(env->hflags & HF_LMA_MASK);
> +        assert(pae_enabled);
> +        return 512;
> +#endif
> +    case 3:
> +        assert(pae_enabled);
> +#ifdef TARGET_X86_64
> +        if (env->hflags & HF_LMA_MASK) {
> +            return 512;
> +        } else
> +#endif
> +        {
> +            return 4;
> +        }
> +    case 2:
> +    case 1:
> +        return pae_enabled ? 512 : 1024;
> +    default:
> +        g_assert_not_reached();
> +    }
> +    return -1;
> +}
> +
> +/**
> + * x86_pte_leaf_page_size - Return the page size of a leaf entry,
> + *                          given the height and CPU state
> + *
> + * @cs - CPU state
> + * @height - height of the page table tree to query, where the leaves
> + *          are 1.
> + *
> + * Returns a value greater than zero on success, -1 on error.
> + */
> +uint64_t x86_pte_leaf_page_size(CPUState *cs, int height)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    bool pae_enabled = env->cr[4] & CR4_PAE_MASK;
> +
> +    assert(height < 6);
> +    assert(height > 0);
> +
> +    switch (height) {
> +#ifdef TARGET_X86_64
> +    case 5:
> +        assert(pae_enabled);
> +        assert(env->cr[4] & CR4_LA57_MASK);
> +        assert(env->hflags & HF_LMA_MASK);
> +        return 1ULL << 48;
> +    case 4:
> +        assert(pae_enabled);
> +        assert(env->hflags & HF_LMA_MASK);
> +        return 1ULL << 39;
> +#endif
> +    case 3:
> +        assert(pae_enabled);
> +        return 1 << 30;
> +    case 2:
> +        if (pae_enabled) {
> +            return 1 << 21;
> +        } else {
> +            return 1 << 22;
> +        }
> +    case 1:
> +        return 4096;
> +    default:
> +        g_assert_not_reached();
> +    }
> +    return -1;
> +}
> +
> +/*
> + * Given a CPU state and height, return the number of bits
> + * to shift right/left in going from virtual to PTE index
> + * and vice versa, the number of useful bits.
> + */
> +static void _mmu_decode_va_parameters(CPUState *cs, int height,
> +                                      int *shift, int *width)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    int _shift = 0;
> +    int _width = 0;
> +    bool pae_enabled = env->cr[4] & CR4_PAE_MASK;
> +
> +    switch (height) {
> +    case 5:
> +        _shift = 48;
> +        _width = 9;
> +        break;
> +    case 4:
> +        _shift = 39;
> +        _width = 9;
> +        break;
> +    case 3:
> +        _shift = 30;
> +        _width = 9;
> +        break;
> +    case 2:
> +        /* 64 bit page tables shift from 30->21 bits here */
> +        if (pae_enabled) {
> +            _shift = 21;
> +            _width = 9;
> +        } else {
> +            /* 32 bit page tables shift from 32->22 bits */
> +            _shift = 22;
> +            _width = 10;
> +        }
> +        break;
> +    case 1:
> +        _shift = 12;
> +        if (pae_enabled) {
> +            _width = 9;
> +        } else {
> +            _width = 10;
> +        }
> +
> +        break;
> +    default:
> +        g_assert_not_reached();
> +    }
> +
> +    if (shift) {
> +        *shift = _shift;
> +    }
> +
> +    if (width) {
> +        *width = _width;
> +    }
> +}
> +
> +/**
> + * get_pte - Copy the contents of the page table entry at node[i] into pt_entry.
> + *           Optionally, add the relevant bits to the virtual address in
> + *           vaddr_pte.
> + *
> + * @cs - CPU state
> + * @node - physical address of the current page table node
> + * @i - index (in page table entries, not bytes) of the page table
> + *      entry, within node
> + * @height - height of node within the tree (leaves are 1, not 0)
> + * @pt_entry - Poiter to a PTE_t, stores the contents of the page table entry
> + * @vaddr_parent - The virtual address bits already translated in walking the
> + *                 page table to node.  Optional: only used if vaddr_pte is set.
> + * @vaddr_pte - Optional pointer to a variable storing the virtual address bits
> + *              translated by node[i].
> + * @pte_paddr - Pointer to the physical address of the PTE within node.
> + *              Optional parameter.
> + */
> +void
> +x86_get_pte(CPUState *cs, hwaddr node, int i, int height,
> +            PTE_t *pt_entry, vaddr vaddr_parent, vaddr *vaddr_pte,
> +            hwaddr *pte_paddr)
> +
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    int32_t a20_mask = x86_get_a20_mask(env);
> +    hwaddr pte;
> +
> +    if (env->hflags & HF_LMA_MASK) {
> +        /* 64 bit */
> +        int pte_width = 8;
> +        pte = (node + (i * pte_width)) & a20_mask;
> +        pt_entry->pte64_t = address_space_ldq(cs->as, pte,
> +                                              MEMTXATTRS_UNSPECIFIED, NULL);
> +    } else {
> +        /* 32 bit */
> +        int pte_width = 4;
> +        pte = (node + (i * pte_width)) & a20_mask;
> +        pt_entry->pte32_t = address_space_ldl(cs->as, pte,
> +                                              MEMTXATTRS_UNSPECIFIED, NULL);
> +    }
> +
> +    if (vaddr_pte) {
> +        int shift = 0;
> +        _mmu_decode_va_parameters(cs, height, &shift, NULL);
> +        *vaddr_pte = vaddr_parent | ((i & 0x1ffULL) << shift);
> +    }
> +
> +    if (pte_paddr) {
> +        *pte_paddr = pte;
> +    }
> +}
> +
> +
> +static bool
> +mmu_pte_check_bits(CPUState *cs, PTE_t *pte, int64_t mask)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    if (env->hflags & HF_LMA_MASK) {
> +        return pte->pte64_t & mask;
> +    } else {
> +        return pte->pte32_t & mask;
> +    }
> +}
> +
> +/**
> + * x86_pte_present - Return true if the pte is marked 'present'
> + */
> +bool
> +x86_pte_present(CPUState *cs, PTE_t *pte)
> +{
> +    return mmu_pte_check_bits(cs, pte, PG_PRESENT_MASK);
> +}
> +
> +/**
> + * x86_pte_leaf - Return true if the pte is
> + *                a page table leaf, false if
> + *                the pte points to another
> + *                node in the radix tree.
> + */
> +bool
> +x86_pte_leaf(CPUState *cs, int height, PTE_t *pte)
> +{
> +    return height == 1 || mmu_pte_check_bits(cs, pte, PG_PSE_MASK);
> +}
> +
> +/**
> + * x86_pte_child - Returns the physical address
> + *                 of a radix tree node pointed to by pte.
> + *
> + * @cs - CPU state
> + * @pte - The page table entry
> + * @height - The height in the tree of pte
> + *
> + * Returns the physical address stored in pte on success,
> + *     -1 on error.
> + */
> +hwaddr
> +x86_pte_child(CPUState *cs, PTE_t *pte, int height)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    bool pae_enabled = env->cr[4] & CR4_PAE_MASK;
> +    int32_t a20_mask = x86_get_a20_mask(env);
> +
> +    switch (height) {
> +#ifdef TARGET_X86_64
> +    case 5:
> +        assert(env->cr[4] & CR4_LA57_MASK);
> +    case 4:
> +        assert(env->hflags & HF_LMA_MASK);
> +        /* assert(pae_enabled); */
> +        /* Fall through */
> +#endif
> +    case 3:
> +        assert(pae_enabled);
> +#ifdef TARGET_X86_64
> +        if (env->hflags & HF_LMA_MASK) {
> +            return (pte->pte64_t & PG_ADDRESS_MASK) & a20_mask;
> +        } else
> +#endif
> +        {
> +            return (pte->pte64_t & ~0xfff) & a20_mask;
> +        }
> +    case 2:
> +    case 1:
> +        if (pae_enabled) {
> +            return (pte->pte64_t & PG_ADDRESS_MASK) & a20_mask;
> +        } else {
> +            return (pte->pte32_t & ~0xfff) & a20_mask;
> +        }
> +    default:
> +        g_assert_not_reached();
> +    }
> +    return -1;
> +}
> +
>   /* PAE Paging or IA-32e Paging */
>   static void walk_pte(MemoryMappingList *list, AddressSpace *as,
>                        hwaddr pte_start_addr,
> @@ -313,4 +663,3 @@ bool x86_cpu_get_memory_mapping(CPUState *cs, MemoryMappingList *list,
>   
>       return true;
>   }
> -
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 914bef442c..8bd6164b68 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -8305,6 +8305,17 @@ static const struct SysemuCPUOps i386_sysemu_ops = {
>       .write_elf32_qemunote = x86_cpu_write_elf32_qemunote,
>       .write_elf64_qemunote = x86_cpu_write_elf64_qemunote,
>       .legacy_vmsd = &vmstate_x86_cpu,
> +    .page_table_root = &x86_page_table_root,
> +    .page_table_entries_per_node = &x86_page_table_entries_per_node,
> +    .get_pte = &x86_get_pte,
> +    .pte_present = &x86_pte_present,
> +    .pte_leaf = &x86_pte_leaf,
> +    .pte_child = &x86_pte_child,
> +    .pte_leaf_page_size = &x86_pte_leaf_page_size,
> +    .pte_flags = &x86_pte_flags,
> +    .mon_init_page_table_iterator = &x86_mon_init_page_table_iterator,
> +    .mon_info_pg_print_header = &x86_mon_info_pg_print_header,
> +    .mon_flush_page_print_state = &x86_mon_flush_print_pg_state,
>   };
>   #endif
>   
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index c64ef0c1a2..cbb6f6fc4d 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -21,6 +21,7 @@
>   #define I386_CPU_H
>   
>   #include "sysemu/tcg.h"
> +#include "hw/core/sysemu-cpu-ops.h"
>   #include "cpu-qom.h"
>   #include "kvm/hyperv-proto.h"
>   #include "exec/cpu-defs.h"
> @@ -2150,8 +2151,22 @@ int x86_cpu_write_elf64_qemunote(WriteCoreDumpFunction f, CPUState *cpu,
>   int x86_cpu_write_elf32_qemunote(WriteCoreDumpFunction f, CPUState *cpu,
>                                    DumpState *s);
>   
> +hwaddr x86_page_table_root(CPUState *cs, int *height);
> +int x86_page_table_entries_per_node(CPUState *cs, int height);
> +uint64_t x86_pte_leaf_page_size(CPUState *cs, int height);
> +void x86_get_pte(CPUState *cs, hwaddr node, int i, int height,
> +                 PTE_t *pt_entry, vaddr vaddr_parent, vaddr *vaddr_pte,
> +                 hwaddr *pte_paddr);
> +bool x86_pte_present(CPUState *cs, PTE_t *pte);
> +bool x86_pte_leaf(CPUState *cs, int height, PTE_t *pte);
> +hwaddr x86_pte_child(CPUState *cs, PTE_t *pte, int height);
> +uint64_t x86_pte_flags(uint64_t pte);
>   bool x86_cpu_get_memory_mapping(CPUState *cpu, MemoryMappingList *list,
>                                   Error **errp);
> +bool x86_mon_init_page_table_iterator(Monitor *mon,
> +                                      struct mem_print_state *state);
> +void x86_mon_info_pg_print_header(Monitor *mon, struct mem_print_state *state);
> +bool x86_mon_flush_print_pg_state(CPUState *cs, struct mem_print_state *state);
>   
>   void x86_cpu_dump_state(CPUState *cs, FILE *f, int flags);
>   
> diff --git a/target/i386/monitor.c b/target/i386/monitor.c
> index 2d766b2637..65e82e73e8 100644
> --- a/target/i386/monitor.c
> +++ b/target/i386/monitor.c
> @@ -32,6 +32,171 @@
>   #include "qapi/qapi-commands-misc-target.h"
>   #include "qapi/qapi-commands-misc.h"
>   
> +
> +/********************* x86 specific hooks for printing page table stuff ****/
> +
> +const char *names[7] = {(char *)NULL, "PTE", "PDE", "PDP", "PML4", "Pml5",
> +                        (char *)NULL};
> +static char *pg_bits(hwaddr ent)
> +{
> +    static char buf[32];
> +    snprintf(buf, 32, "%c%c%c%c%c%c%c%c%c%c",
> +            ent & PG_NX_MASK ? 'X' : '-',
> +            ent & PG_GLOBAL_MASK ? 'G' : '-',
> +            ent & PG_PSE_MASK ? 'S' : '-',
> +            ent & PG_DIRTY_MASK ? 'D' : '-',
> +            ent & PG_ACCESSED_MASK ? 'A' : '-',
> +            ent & PG_PCD_MASK ? 'C' : '-',
> +            ent & PG_PWT_MASK ? 'T' : '-',
> +            ent & PG_USER_MASK ? 'U' : '-',
> +            ent & PG_RW_MASK ? 'W' : '-',
> +            ent & PG_PRESENT_MASK ? 'P' : '-');
> +    return buf;
> +}
> +
> +bool x86_mon_init_page_table_iterator(Monitor *mon,
> +                                      struct mem_print_state *state)
> +{
> +    CPUArchState *env;
> +    state->mon = mon;
> +    state->flush_interior = false;
> +    state->require_physical_contiguity = false;
> +
> +    for (int i = 0; i < MAX_HEIGHT; i++) {
> +        state->vstart[i] = -1;
> +        state->last_offset[i] = 0;
> +    }
> +    state->start_height = 0;
> +
> +    env = mon_get_cpu_env(mon);
> +    if (!env) {
> +        monitor_printf(mon, "No CPU available\n");
> +        return false;
> +    }
> +    state->env = env;
> +
> +    if (!(env->cr[0] & CR0_PG_MASK)) {
> +        monitor_printf(mon, "PG disabled\n");
> +        return false;
> +    }
> +
> +    /* set va and pa width */
> +    if (env->cr[4] & CR4_PAE_MASK) {
> +        state->paw = 13;
> +#ifdef TARGET_X86_64
> +        if (env->hflags & HF_LMA_MASK) {
> +            if (env->cr[4] & CR4_LA57_MASK) {
> +                state->vaw = 15;
> +                state->max_height = 5;
> +            } else {
> +                state->vaw = 12;
> +                state->max_height = 4;
> +            }
> +        } else
> +#endif
> +        {
> +            state->vaw = 8;
> +            state->max_height = 3;
> +        }
> +    } else {
> +        state->max_height = 2;
> +        state->vaw = 8;
> +        state->paw = 8;
> +    }
> +
> +    return true;
> +}
> +
> +void x86_mon_info_pg_print_header(Monitor *mon, struct mem_print_state *state)
> +{
> +    /* Header line */
> +    monitor_printf(mon, "%-*s %-13s %-10s %*s%s\n",
> +                   3 + 2 * (state->vaw - 3), "VPN range",
> +                   "Entry", "Flags",
> +                   2 * (state->max_height - 1), "", "Physical page(s)");
> +}
> +
> +
> +static void pg_print(CPUState *cs, Monitor *mon, uint64_t pt_ent,
> +                     target_ulong vaddr_s, target_ulong vaddr_l,
> +                     hwaddr paddr_s, hwaddr paddr_l,
> +                     int offset_s, int offset_l,
> +                     int height, int max_height, int vaw, int paw,
> +                     bool is_leaf)
> +
> +{
> +    char buf[128];
> +    char *pos = buf, *end = buf + sizeof(buf);
> +    target_ulong size = x86_pte_leaf_page_size(cs, height);
> +
> +    /* VFN range */
> +    pos += snprintf(pos, end - pos, "%*s[%0*"PRIx64"-%0*"PRIx64"] ",
> +                    (max_height - height) * 2, "",
> +                    vaw - 3, (uint64_t)vaddr_s >> 12,
> +                    vaw - 3, ((uint64_t)vaddr_l + size - 1) >> 12);
> +
> +    /* Slot */
> +    if (vaddr_s == vaddr_l) {
> +        pos += snprintf(pos, end - pos, "%4s[%03x]    ",
> +                       names[height], offset_s);
> +    } else {
> +        pos += snprintf(pos, end - pos, "%4s[%03x-%03x]",
> +                       names[height], offset_s, offset_l);
> +    }
> +
> +    /* Flags */
> +    pos += snprintf(pos, end - pos, " %s", pg_bits(pt_ent));
> +
> +
> +    /* Range-compressed PFN's */
> +    if (is_leaf) {
> +        if (vaddr_s == vaddr_l) {
> +            pos += snprintf(pos, end - pos, " %0*"PRIx64,
> +                            paw - 3, (uint64_t)paddr_s >> 12);
> +        } else {
> +            pos += snprintf(pos, end - pos, " %0*"PRIx64"-%0*"PRIx64,
> +                            paw - 3, (uint64_t)paddr_s >> 12,
> +                            paw - 3, (uint64_t)paddr_l >> 12);
> +        }
> +        pos = MIN(pos, end);
> +    }
> +
> +    /* Trim line to fit screen */
> +    if (pos - buf > 79) {
> +        strcpy(buf + 77, "..");
> +    }
> +
> +    monitor_printf(mon, "%s\n", buf);
> +}
> +
> +uint64_t x86_pte_flags(uint64_t pte)
> +{
> +    return pte & (PG_USER_MASK | PG_RW_MASK |
> +                  PG_PRESENT_MASK);
> +}
> +
> +/* Returns true if it emitted anything */
> +bool x86_mon_flush_print_pg_state(CPUState *cs, struct mem_print_state *state)
> +{
> +    bool ret = false;
> +    for (int i = state->start_height; i > 0; i--) {
> +        if (state->vstart[i] == -1) {
> +            break;
> +        }
> +        PTE_t my_pte;
> +        my_pte.pte64_t = state->ent[i];
> +        ret = true;
> +        pg_print(cs, state->mon, state->ent[i],
> +                 state->vstart[i], state->vend[i],
> +                 state->pstart, state->pend,
> +                 state->offset[i], state->last_offset[i],
> +                 i, state->max_height, state->vaw, state->paw,
> +                 x86_pte_leaf(cs, i, &my_pte));
> +    }
> +
> +    return ret;
> +}
> +
>   /* Perform linear address sign extension */
>   static hwaddr addr_canonical(CPUArchState *env, hwaddr addr)
>   {

On Thu, Jun 06, 2024 at 10:02:48AM -0400, Don Porter wrote:
> The new "info pg" monitor command prints the current page table,
> including virtual address ranges, flag bits, and snippets of physical
> page numbers.  Completely filled regions of the page table with
> compatible flags are "folded", with the result that the complete
> output for a freshly booted x86-64 Linux VM can fit in a single
> terminal window.  The output looks like this:
> 
> VPN range             Entry         Flags            Physical page
> [7f0000000-7f0000000] PML4[0fe]     ---DA--UWP
>   [7f28c0000-7f28fffff]  PDP[0a3]     ---DA--UWP
>     [7f28c4600-7f28c47ff]  PDE[023]     ---DA--UWP
>       [7f28c4655-7f28c4656]  PTE[055-056] X--D---U-P 0000007f14-0000007f15
>       [7f28c465b-7f28c465b]  PTE[05b]     ----A--U-P 0000001cfc
> ...
> [ff8000000-ff8000000] PML4[1ff]     ---DA--UWP
>   [ffff80000-ffffbffff]  PDP[1fe]     ---DA---WP
>     [ffff81000-ffff81dff]  PDE[008-00e] -GSDA---WP 0000001000-0000001dff
>   [ffffc0000-fffffffff]  PDP[1ff]     ---DA--UWP
>     [ffffff400-ffffff5ff]  PDE[1fa]     ---DA--UWP
>       [ffffff5fb-ffffff5fc]  PTE[1fb-1fc] XG-DACT-WP 00000fec00 00000fee00
>     [ffffff600-ffffff7ff]  PDE[1fb]     ---DA--UWP
>       [ffffff600-ffffff600]  PTE[000]     -G-DA--U-P 0000001467
> 
> This draws heavy inspiration from Austin Clements' original patch.
> 
> This also adds a generic page table walker, which other monitor
> and execution commands will be migrated to in subsequent patches.
> 
> Signed-off-by: Don Porter <porter@cs.unc.edu>
> ---
>  hmp-commands-info.hx              |  13 ++
>  hw/core/cpu-sysemu.c              | 140 ++++++++++++
>  include/hw/core/cpu.h             |  34 ++-
>  include/hw/core/sysemu-cpu-ops.h  | 156 +++++++++++++
>  include/monitor/hmp-target.h      |   1 +
>  monitor/hmp-cmds-target.c         | 198 +++++++++++++++++
>  target/i386/arch_memory_mapping.c | 351 +++++++++++++++++++++++++++++-
>  target/i386/cpu.c                 |  11 +
>  target/i386/cpu.h                 |  15 ++
>  target/i386/monitor.c             | 165 ++++++++++++++
>  10 files changed, 1082 insertions(+), 2 deletions(-)
> +
> +void hmp_info_pg(Monitor *mon, const QDict *qdict)
> +{
> +    struct mem_print_state state;
> +
> +    CPUState *cs = mon_get_cpu(mon);
> +    if (!cs) {
> +        monitor_printf(mon, "Unable to get CPUState.  Internal error\n");
> +        return;
> +    }
> +
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +
> +    if ((!cc->sysemu_ops->pte_child)
> +        || (!cc->sysemu_ops->pte_leaf)
> +        || (!cc->sysemu_ops->pte_leaf_page_size)
> +        || (!cc->sysemu_ops->page_table_entries_per_node)
> +        || (!cc->sysemu_ops->pte_flags)
> +        || (!cc->sysemu_ops->mon_init_page_table_iterator)
> +        || (!cc->sysemu_ops->mon_info_pg_print_header)
> +        || (!cc->sysemu_ops->mon_flush_page_print_state)) {
> +        monitor_printf(mon, "Info pg unsupported on this ISA\n");
> +        return;
> +    }
> +
> +    if (!cc->sysemu_ops->mon_init_page_table_iterator(mon, &state)) {
> +        monitor_printf(mon, "Unable to initialize page table iterator\n");
> +        return;
> +    }
> +
> +    state.flush_interior = true;
> +    state.require_physical_contiguity = true;
> +    state.flusher = cc->sysemu_ops->mon_flush_page_print_state;
> +
> +    cc->sysemu_ops->mon_info_pg_print_header(mon, &state);
> +
> +    /*
> +     * We must visit interior entries to get the hierarchy, but
> +     * can skip not present mappings
> +     */
> +    for_each_pte(cs, &compressing_iterator, &state, true, false);
> +
> +    /* Print last entry, if one present */
> +    cc->sysemu_ops->mon_flush_page_print_state(cs, &state);
> +}

Please don't add new HMP commands that don't have a QMP
equivalent.

This should be adding an 'x-query-pg' QMP command, which
returns HumanReadableText, and then call that from the HMP

There is guidance on this here:

  https://www.qemu.org/docs/master/devel/writing-monitor-commands.html#writing-a-debugging-aid-returning-unstructured-text

If you need more real examples, look at the various
'x-query-XXXX' commands in qapi/machine.json  and
their impl.


With regards,
Daniel

On 6/6/24 07:02, Don Porter wrote:
> +/**
> + * _for_each_pte - recursive helper function
> + *
> + * @cs - CPU state
> + * @fn(cs, data, pte, vaddr, height) - User-provided function to call on each
> + *                                     pte.
> + *   * @cs - pass through cs
> + *   * @data - user-provided, opaque pointer
> + *   * @pte - current pte
> + *   * @vaddr_in - virtual address translated by pte
> + *   * @height - height in the tree of pte
> + * @data - user-provided, opaque pointer, passed to fn()
> + * @visit_interior_nodes - if true, call fn() on page table entries in
> + *                         interior nodes.  If false, only call fn() on page
> + *                         table entries in leaves.
> + * @visit_not_present - if true, call fn() on entries that are not present.
> + *                         if false, visit only present entries.
> + * @node - The physical address of the current page table radix tree node
> + * @vaddr_in - The virtual address bits translated in walking the page
> + *          table to node
> + * @height - The height of node in the radix tree
> + *
> + * height starts at the max and counts down.
> + * In a 4 level x86 page table, pml4e is level 4, pdpe is level 3,
> + *  pde is level 2, and pte is level 1
> + *
> + * Returns true on success, false on error.
> + */
> +static bool
> +_for_each_pte(CPUState *cs,

External identifiers beginning with "_[a-z]" are reserved.  While this is not external, 
and so is technically ok, it is still not a great idea.  Use for_each_pte_$SUFFIX, with 
SUFFIX as int, internal, recurse or something.


> +              int (*fn)(CPUState *cs, void *data, PTE_t *pte,
> +                        vaddr vaddr_in, int height, int offset),
> +              void *data, bool visit_interior_nodes,
> +              bool visit_not_present, hwaddr node,
> +              vaddr vaddr_in, int height)
> +{
> +    int ptes_per_node;
> +    int i;
> +
> +    assert(height > 0);
> +
> +    CPUClass *cc = CPU_GET_CLASS(cs);
> +
> +    if ((!cc->sysemu_ops->page_table_entries_per_node)
> +        || (!cc->sysemu_ops->get_pte)
> +        || (!cc->sysemu_ops->pte_present)
> +        || (!cc->sysemu_ops->pte_leaf)
> +        || (!cc->sysemu_ops->pte_child)) {
> +        return false;
> +    }

Probably move this check to the non-recursive function, since it only needs to be done 
once.  Following a check for page_table_root, should the rest be asserts?  I.e. if a 
target implements one hook, it must implement them all?

CPU_GET_CLASS is non-trivial: it is cached in cs->cc.
It seems like you should cache cs->cc->sysemu_ops in a local to avoid constantly reloading 
the pointer across the loop.

> +    ptes_per_node = cc->sysemu_ops->page_table_entries_per_node(cs, height);

It would be better if the entire page table format were computed by page_table_root. 
Perhaps fill in a whole structure rather than just height.

> +    for (i = 0; i < ptes_per_node; i++) {
> +        PTE_t pt_entry;
> +        vaddr vaddr_i;
> +        bool pte_present;
> +
> +        cc->sysemu_ops->get_pte(cs, node, i, height, &pt_entry, vaddr_in,
> +                                &vaddr_i, NULL);
> +        pte_present = cc->sysemu_ops->pte_present(cs, &pt_entry);
> +
> +        if (pte_present || visit_not_present) {
> +            if ((!pte_present) || cc->sysemu_ops->pte_leaf(cs, height,
> +                                                           &pt_entry)) {

Again, better to fill in a structure in get_pte rather than make 4 calls for vaddr, 
present, leaf, child.

Drop the unnecessary (), e.g. around !pte_present.

> +/* Intended to become a generic PTE type */
> +typedef union PTE {
> +    uint64_t pte64_t;
> +    uint32_t pte32_t;
> +} PTE_t;

While not yet supported by qemu, the latest Arm v9.4 document contains a 128-bit PTE.
Don't give the tag and the typedef different names.
Avoid "_t" as that's POSIX reserved namespace.

I know naming is hard, but there are many kinds of PTE in qemu -- better to use something 
more descriptive.  Perhaps "QemuPageWalkerPTE"?

> +bool for_each_pte(CPUState *cs,
> +                  int (*fn)(CPUState *cs, void *data, PTE_t *pte, vaddr vaddr,
> +                            int height, int offset), void *data,
> +                  bool visit_interior_nodes, bool visit_not_present);

Use a typedef for the callback function.
qemu_page_walker_for_each?

> +
> +
>   /**
>    * CPUDumpFlags:
>    * @CPU_DUMP_CODE:
> diff --git a/include/hw/core/sysemu-cpu-ops.h b/include/hw/core/sysemu-cpu-ops.h
> index 24d003fe04..eb16a1c3e2 100644
> --- a/include/hw/core/sysemu-cpu-ops.h
> +++ b/include/hw/core/sysemu-cpu-ops.h
> @@ -12,6 +12,39 @@
>   
>   #include "hw/core/cpu.h"
>   
> +/* Maximum supported page table height - currently x86 at 5 */
> +#define MAX_HEIGHT 5
> +
> +/*
> + * struct mem_print_state: Used by monitor in walking page tables.
> + */
> +struct mem_print_state {
> +    Monitor *mon;
> +    CPUArchState *env;
> +    int vaw, paw; /* VA and PA width in characters */
> +    int max_height;
> +    bool (*flusher)(CPUState *cs, struct mem_print_state *state);
> +    bool flush_interior; /* If false, only call flusher() on leaves */
> +    bool require_physical_contiguity;
> +    /*
> +     * The height at which we started accumulating ranges, i.e., the
> +     * next height we need to print once we hit the end of a
> +     * contiguous range.
> +     */
> +    int start_height;
> +    /*
> +     * For compressing contiguous ranges, track the
> +     * start and end of the range
> +     */
> +    hwaddr vstart[MAX_HEIGHT + 1]; /* Starting virt. addr. of open pte range */
> +    hwaddr vend[MAX_HEIGHT + 1]; /* Ending virtual address of open pte range */
> +    hwaddr pstart; /* Starting physical address of open pte range */
> +    hwaddr pend; /* Ending physical address of open pte range */
> +    int64_t ent[MAX_HEIGHT + 1]; /* PTE contents on current root->leaf path */

PTE_t (or the rename)?

> +    int offset[MAX_HEIGHT + 1]; /* PTE range starting offsets */
> +    int last_offset[MAX_HEIGHT + 1]; /* PTE range ending offsets */
> +};
> +
>   /*
>    * struct SysemuCPUOps: System operations specific to a CPU class
>    */
> @@ -87,6 +120,129 @@ typedef struct SysemuCPUOps {
>        */
>       const VMStateDescription *legacy_vmsd;
>   
> +    /**
> +     * page_table_root - Given a CPUState, return the physical address
> +     *                    of the current page table root, as well as
> +     *                    write the height of the tree into *height.
> +     *
> +     * @cs - CPU state
> +
> +     * @height - a pointer to an integer, to store the page table tree
> +     *           height
> +     *
> +     * Returns a hardware address on success.  Should not fail (i.e.,
> +     * caller is responsible to ensure that a page table is actually
> +     * present).
> +     */
> +    hwaddr (*page_table_root)(CPUState *cs, int *height);

There may be two page table roots on Arm, depending on the cpu state and the virtual 
address.  The shape of the two page tables are independent so...


> +
> +    /**
> +     * page_table_entries_per_node - Return the number of entries in a
> +     *                                   page table node for the CPU
> +     *                                   at a given height.
> +     *
> +     * @cs - CPU state
> +     * @height - height of the page table tree to query, where the leaves
> +     *          are 1.
> +     *
> +     * Returns a value greater than zero on success, -1 on error.
> +     */
> +    int (*page_table_entries_per_node)(CPUState *cs, int height);

... implementing this independently from page_table_root is not possible.


> +
> +    /**
> +     * @mon_init_page_table_iterator: Callback to configure a page table
> +     * iterator for use by a monitor function.
> +     * Returns true on success, false if not supported (e.g., no paging disabled
> +     * or not implemented on this CPU).
> +     */
> +    bool (*mon_init_page_table_iterator)(Monitor *mon,
> +                                         struct mem_print_state *state);

I don't understand the purpose of this one as a target-specific hook.

> +    /**
> +     * @flush_page_table_iterator_state: Prints the last entry,
> +     * if one is present.  Useful for iterators that aggregate information
> +     * across page table entries.
> +     */
> +    bool (*mon_flush_page_print_state)(CPUState *cs,
> +                                       struct mem_print_state *state);

Is this specific to "info pg" or not?
It appears to be, but the description suggests it is not.


r~

On 6/6/24 07:02, Don Porter wrote:
> +/**
> + * get_pte - Copy the contents of the page table entry at node[i] into pt_entry.
> + *           Optionally, add the relevant bits to the virtual address in
> + *           vaddr_pte.
> + *
> + * @cs - CPU state
> + * @node - physical address of the current page table node
> + * @i - index (in page table entries, not bytes) of the page table
> + *      entry, within node
> + * @height - height of node within the tree (leaves are 1, not 0)
> + * @pt_entry - Poiter to a PTE_t, stores the contents of the page table entry
> + * @vaddr_parent - The virtual address bits already translated in walking the
> + *                 page table to node.  Optional: only used if vaddr_pte is set.
> + * @vaddr_pte - Optional pointer to a variable storing the virtual address bits
> + *              translated by node[i].
> + * @pte_paddr - Pointer to the physical address of the PTE within node.
> + *              Optional parameter.
> + */
> +void
> +x86_get_pte(CPUState *cs, hwaddr node, int i, int height,
> +            PTE_t *pt_entry, vaddr vaddr_parent, vaddr *vaddr_pte,
> +            hwaddr *pte_paddr)
> +
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    int32_t a20_mask = x86_get_a20_mask(env);
> +    hwaddr pte;
> +
> +    if (env->hflags & HF_LMA_MASK) {
> +        /* 64 bit */
> +        int pte_width = 8;
> +        pte = (node + (i * pte_width)) & a20_mask;
> +        pt_entry->pte64_t = address_space_ldq(cs->as, pte,
> +                                              MEMTXATTRS_UNSPECIFIED, NULL);
> +    } else {
> +        /* 32 bit */
> +        int pte_width = 4;
> +        pte = (node + (i * pte_width)) & a20_mask;
> +        pt_entry->pte32_t = address_space_ldl(cs->as, pte,
> +                                              MEMTXATTRS_UNSPECIFIED, NULL);
> +    }
> +
> +    if (vaddr_pte) {
> +        int shift = 0;
> +        _mmu_decode_va_parameters(cs, height, &shift, NULL);
> +        *vaddr_pte = vaddr_parent | ((i & 0x1ffULL) << shift);
> +    }
> +
> +    if (pte_paddr) {
> +        *pte_paddr = pte;
> +    }
> +}

This fails to recurse with nested page tables, which definitely breaks the TCG walker.


r~

On 6/7/24 3:16 AM, Daniel P. Berrangé wrote:
> On Thu, Jun 06, 2024 at 10:02:48AM -0400, Don Porter wrote:
> Please don't add new HMP commands that don't have a QMP
> equivalent.
>
> This should be adding an 'x-query-pg' QMP command, which
> returns HumanReadableText, and then call that from the HMP
>
> There is guidance on this here:
>
>    https://www.qemu.org/docs/master/devel/writing-monitor-commands.html#writing-a-debugging-aid-returning-unstructured-text
>
> If you need more real examples, look at the various
> 'x-query-XXXX' commands in qapi/machine.json  and
> their impl.

Thank you both for the pointers.  This makes sense to me;
outputting a string is much cleaner.  Will implement in v4...

-dp

Hi Richard,

Thank you for all of the helpful comments!  v4 will be much cleaner as a 
result.

A few follow-ups inline.

On 6/7/24 12:57 PM, Richard Henderson wrote:
> On 6/6/24 07:02, Don Porter wrote:
>> +
>> +    /**
>> +     * @mon_init_page_table_iterator: Callback to configure a page 
>> table
>> +     * iterator for use by a monitor function.
>> +     * Returns true on success, false if not supported (e.g., no 
>> paging disabled
>> +     * or not implemented on this CPU).
>> +     */
>> +    bool (*mon_init_page_table_iterator)(Monitor *mon,
>> +                                         struct mem_print_state 
>> *state);
>
> I don't understand the purpose of this one as a target-specific hook.

The iterator needs some architecture-specific initialization, such as 
getting the virtual
and physical address width.

>
>> +    /**
>> +     * @flush_page_table_iterator_state: Prints the last entry,
>> +     * if one is present.  Useful for iterators that aggregate 
>> information
>> +     * across page table entries.
>> +     */
>> +    bool (*mon_flush_page_print_state)(CPUState *cs,
>> +                                       struct mem_print_state *state);
>
> Is this specific to "info pg" or not?
> It appears to be, but the description suggests it is not.

It is.

Thank you,

Don

On 6/7/24 1:43 PM, Richard Henderson wrote:
> On 6/6/24 07:02, Don Porter wrote:
>> +/**
>> + * get_pte - Copy the contents of the page table entry at node[i] 
>> into pt_entry.
>> + *           Optionally, add the relevant bits to the virtual 
>> address in
>> + *           vaddr_pte.
>> + *
>> + * @cs - CPU state
>> + * @node - physical address of the current page table node
>> + * @i - index (in page table entries, not bytes) of the page table
>> + *      entry, within node
>> + * @height - height of node within the tree (leaves are 1, not 0)
>> + * @pt_entry - Poiter to a PTE_t, stores the contents of the page 
>> table entry
>> + * @vaddr_parent - The virtual address bits already translated in 
>> walking the
>> + *                 page table to node.  Optional: only used if 
>> vaddr_pte is set.
>> + * @vaddr_pte - Optional pointer to a variable storing the virtual 
>> address bits
>> + *              translated by node[i].
>> + * @pte_paddr - Pointer to the physical address of the PTE within node.
>> + *              Optional parameter.
>> + */
>> +void
>> +x86_get_pte(CPUState *cs, hwaddr node, int i, int height,
>> +            PTE_t *pt_entry, vaddr vaddr_parent, vaddr *vaddr_pte,
>> +            hwaddr *pte_paddr)
>> +
>> +{
>> +    X86CPU *cpu = X86_CPU(cs);
>> +    CPUX86State *env = &cpu->env;
>> +    int32_t a20_mask = x86_get_a20_mask(env);
>> +    hwaddr pte;
>> +
>> +    if (env->hflags & HF_LMA_MASK) {
>> +        /* 64 bit */
>> +        int pte_width = 8;
>> +        pte = (node + (i * pte_width)) & a20_mask;
>> +        pt_entry->pte64_t = address_space_ldq(cs->as, pte,
>> + MEMTXATTRS_UNSPECIFIED, NULL);
>> +    } else {
>> +        /* 32 bit */
>> +        int pte_width = 4;
>> +        pte = (node + (i * pte_width)) & a20_mask;
>> +        pt_entry->pte32_t = address_space_ldl(cs->as, pte,
>> + MEMTXATTRS_UNSPECIFIED, NULL);
>> +    }
>> +
>> +    if (vaddr_pte) {
>> +        int shift = 0;
>> +        _mmu_decode_va_parameters(cs, height, &shift, NULL);
>> +        *vaddr_pte = vaddr_parent | ((i & 0x1ffULL) << shift);
>> +    }
>> +
>> +    if (pte_paddr) {
>> +        *pte_paddr = pte;
>> +    }
>> +}
>
> This fails to recurse with nested page tables, which definitely breaks 
> the TCG walker.

Hi Richard,

Thank you again for all of the advice and feedback.

What do you think the correct semantics should be for nested paging?

My understanding is that the current 'info mem' command on x86 does not 
recur on nested page tables, but this does seem like a useful 
extension.  Same for 'info tlb'.

In the case of 'info pg', I might want to print each page table 
separately, rather than a combined/shadow view.

My reading of the tcg code is that it also walks the guest page tables 
first, then uses probe_access_full() to query the guest->host physical 
translation, but I may be misunderstanding the code: 
https://github.com/qemu/qemu/blob/046a64b9801343e2e89eef10c7a48eec8d8c0d4f/target/i386/tcg/sysemu/excp_helper.c#L432

In patch 6 of the series, I replace the chunk of mmu_translate() in tcg 
that walks the guest page tables, but leave the portion alone that does 
the nested page walk.

I'm open to implementing a nested walker, but it might be better not to 
add more functionality/changes to this patch series.

Thank you,

Don

On 6/14/24 14:14, Don Porter wrote:
> On 6/7/24 1:43 PM, Richard Henderson wrote:
>> On 6/6/24 07:02, Don Porter wrote:
>>> +/**
>>> + * get_pte - Copy the contents of the page table entry at node[i] into pt_entry.
>>> + *           Optionally, add the relevant bits to the virtual address in
>>> + *           vaddr_pte.
>>> + *
>>> + * @cs - CPU state
>>> + * @node - physical address of the current page table node
>>> + * @i - index (in page table entries, not bytes) of the page table
>>> + *      entry, within node
>>> + * @height - height of node within the tree (leaves are 1, not 0)
>>> + * @pt_entry - Poiter to a PTE_t, stores the contents of the page table entry
>>> + * @vaddr_parent - The virtual address bits already translated in walking the
>>> + *                 page table to node.  Optional: only used if vaddr_pte is set.
>>> + * @vaddr_pte - Optional pointer to a variable storing the virtual address bits
>>> + *              translated by node[i].
>>> + * @pte_paddr - Pointer to the physical address of the PTE within node.
>>> + *              Optional parameter.
>>> + */
>>> +void
>>> +x86_get_pte(CPUState *cs, hwaddr node, int i, int height,
>>> +            PTE_t *pt_entry, vaddr vaddr_parent, vaddr *vaddr_pte,
>>> +            hwaddr *pte_paddr)
>>> +
>>> +{
>>> +    X86CPU *cpu = X86_CPU(cs);
>>> +    CPUX86State *env = &cpu->env;
>>> +    int32_t a20_mask = x86_get_a20_mask(env);
>>> +    hwaddr pte;
>>> +
>>> +    if (env->hflags & HF_LMA_MASK) {
>>> +        /* 64 bit */
>>> +        int pte_width = 8;
>>> +        pte = (node + (i * pte_width)) & a20_mask;
>>> +        pt_entry->pte64_t = address_space_ldq(cs->as, pte,
>>> + MEMTXATTRS_UNSPECIFIED, NULL);
>>> +    } else {
>>> +        /* 32 bit */
>>> +        int pte_width = 4;
>>> +        pte = (node + (i * pte_width)) & a20_mask;
>>> +        pt_entry->pte32_t = address_space_ldl(cs->as, pte,
>>> + MEMTXATTRS_UNSPECIFIED, NULL);
>>> +    }
>>> +
>>> +    if (vaddr_pte) {
>>> +        int shift = 0;
>>> +        _mmu_decode_va_parameters(cs, height, &shift, NULL);
>>> +        *vaddr_pte = vaddr_parent | ((i & 0x1ffULL) << shift);
>>> +    }
>>> +
>>> +    if (pte_paddr) {
>>> +        *pte_paddr = pte;
>>> +    }
>>> +}
>>
>> This fails to recurse with nested page tables, which definitely breaks the TCG walker.
> 
> Hi Richard,
> 
> Thank you again for all of the advice and feedback.
> 
> What do you think the correct semantics should be for nested paging?

That it works like hardware does.

> My understanding is that the current 'info mem' command on x86 does not recur on nested 
> page tables, but this does seem like a useful extension.  Same for 'info tlb'.

My understanding is that the two existing hmp commands are broken, and that the *only* 
correct page table walker is get_physical_address.

> In the case of 'info pg', I might want to print each page table separately, rather than a 
> combined/shadow view.

Without doing the nested page translation for the page tables themselves, you're not 
looking at the correct page from which to read the PTEs, and reading garbage.

> My reading of the tcg code is that it also walks the guest page tables first, then uses 
> probe_access_full() to query the guest->host physical translation, but I may be 
> misunderstanding the code: 
> https://github.com/qemu/qemu/blob/046a64b9801343e2e89eef10c7a48eec8d8c0d4f/target/i386/tcg/sysemu/excp_helper.c#L432

I'm talking about this, for the page tables themselves:

https://github.com/qemu/qemu/blob/046a64b9801343e2e89eef10c7a48eec8d8c0d4f/target/i386/tcg/sysemu/excp_helper.c#L69

A better example is for ARM, which has had its debug page table walker folded in:

https://github.com/qemu/qemu/blob/046a64b9801343e2e89eef10c7a48eec8d8c0d4f/target/arm/ptw.c#L553

If in_debug, don't use probe_access_full_mmu as a cache (and host page resolution), but 
explicitly recurse on get_phys_addr_gpc.


r~