[RFC,v2,1/2] vhost-vdpa: Implement IOVA->GPA tree

Implements the IOVA->GPA tree for handling mapping, unmapping, and
translations for guest memory regions.

When the guest has overlapping memory regions, an HVA to IOVA translation
may return an incorrect IOVA when searching the IOVA->HVA tree. This is
due to one HVA range being contained (overlapping) in another HVA range
in the IOVA->HVA tree. By creating an IOVA->GPA tree, we can use GPAs to
translate and find the correct IOVA for guest memory regions.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
 hw/virtio/vhost-iova-tree.c | 78 +++++++++++++++++++++++++++++++++++--
 hw/virtio/vhost-iova-tree.h |  5 +++
 hw/virtio/vhost-vdpa.c      | 20 ++++++----
 3 files changed, 92 insertions(+), 11 deletions(-)

On Fri, Oct 4, 2024 at 2:45 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
> Implements the IOVA->GPA tree for handling mapping, unmapping, and
> translations for guest memory regions.
>
> When the guest has overlapping memory regions, an HVA to IOVA translation
> may return an incorrect IOVA when searching the IOVA->HVA tree. This is
> due to one HVA range being contained (overlapping) in another HVA range
> in the IOVA->HVA tree. By creating an IOVA->GPA tree, we can use GPAs to
> translate and find the correct IOVA for guest memory regions.
>

Yes, this first patch is super close to what I meant, just one issue
and a pair of nits here and there.

I'd leave the second patch as an optimization on top, if the numbers
prove that adding the code is worth it.

> Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> ---
>  hw/virtio/vhost-iova-tree.c | 78 +++++++++++++++++++++++++++++++++++--
>  hw/virtio/vhost-iova-tree.h |  5 +++
>  hw/virtio/vhost-vdpa.c      | 20 ++++++----
>  3 files changed, 92 insertions(+), 11 deletions(-)
>
> diff --git a/hw/virtio/vhost-iova-tree.c b/hw/virtio/vhost-iova-tree.c
> index 3d03395a77..e33fd56225 100644
> --- a/hw/virtio/vhost-iova-tree.c
> +++ b/hw/virtio/vhost-iova-tree.c
> @@ -28,12 +28,15 @@ struct VhostIOVATree {
>
>      /* IOVA address to qemu memory maps. */
>      IOVATree *iova_taddr_map;
> +
> +    /* IOVA address to guest memory maps. */
> +    IOVATree *iova_gpa_map;
>  };
>
>  /**
> - * Create a new IOVA tree
> + * Create a new VhostIOVATree
>   *
> - * Returns the new IOVA tree
> + * Returns the new VhostIOVATree
>   */
>  VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, hwaddr iova_last)
>  {
> @@ -44,6 +47,7 @@ VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, hwaddr iova_last)
>      tree->iova_last = iova_last;
>
>      tree->iova_taddr_map = iova_tree_new();
> +    tree->iova_gpa_map = iova_tree_new();
>      return tree;
>  }
>
> @@ -53,6 +57,7 @@ VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, hwaddr iova_last)
>  void vhost_iova_tree_delete(VhostIOVATree *iova_tree)
>  {
>      iova_tree_destroy(iova_tree->iova_taddr_map);
> +    iova_tree_destroy(iova_tree->iova_gpa_map);
>      g_free(iova_tree);
>  }
>
> @@ -71,7 +76,7 @@ const DMAMap *vhost_iova_tree_find_iova(const VhostIOVATree *tree,
>  }
>
>  /**
> - * Allocate a new mapping
> + * Allocate a new mapping in the IOVA->HVA tree
>   *
>   * @tree: The iova tree
>   * @map: The iova map
> @@ -108,3 +113,70 @@ void vhost_iova_tree_remove(VhostIOVATree *iova_tree, DMAMap map)
>  {
>      iova_tree_remove(iova_tree->iova_taddr_map, map);
>  }
> +
> +/**
> + * Find the IOVA address stored from a guest memory address
> + *
> + * @tree: The VhostIOVATree
> + * @map: The map with the guest memory address
> + *
> + * Return the stored mapping, or NULL if not found.
> + */
> +const DMAMap *vhost_iova_gpa_tree_find_iova(const VhostIOVATree *tree,
> +                                            const DMAMap *map)

Nit: Not an english native, but I find vhost_iova_tree should not be
broken for coherency with the rest of the functions. What about
vhost_iova_tree_find_iova_gpa, like _gpa variant?

> +{
> +    return iova_tree_find_iova(tree->iova_gpa_map, map);
> +}
> +
> +/**
> + * Allocate new mappings in the IOVA->HVA & IOVA->GPA trees
> + *
> + * @tree: The VhostIOVATree
> + * @map: The iova map
> + * @gpa: The guest physical address (GPA)
> + *
> + * Returns:
> + * - IOVA_OK if the map fits both containers
> + * - IOVA_ERR_INVALID if the map does not make sense (like size overflow)
> + * - IOVA_ERR_NOMEM if the IOVA->HVA tree cannot allocate more space
> + *
> + * It returns an assigned iova in map->iova if return value is IOVA_OK.
> + */
> +int vhost_iova_tree_map_alloc_gpa(VhostIOVATree *tree, DMAMap *map, hwaddr gpa)
> +{
> +    int ret;
> +
> +    /* Some vhost devices don't like addr 0. Skip first page */
> +    hwaddr iova_first = tree->iova_first ?: qemu_real_host_page_size();
> +
> +    if (map->translated_addr + map->size < map->translated_addr ||
> +        map->perm == IOMMU_NONE) {
> +        return IOVA_ERR_INVALID;
> +    }
> +
> +    /* Allocate a node in the IOVA->HVA tree */
> +    ret = iova_tree_alloc_map(tree->iova_taddr_map, map, iova_first,
> +                              tree->iova_last);

Why not call vhost_iova_tree_map_alloc instead of duplicating it here?

> +    if (unlikely(ret != IOVA_OK)) {
> +        return ret;
> +    }
> +
> +    /* Insert a node in the IOVA->GPA tree */
> +    map->translated_addr = gpa;
> +    return iova_tree_insert(tree->iova_gpa_map, map);
> +}
> +
> +/**
> + * Remove existing mappings from the IOVA->HVA & IOVA->GPA trees
> + *
> + * @iova_tree: The VhostIOVATree
> + * @map: The map to remove
> + */
> +void vhost_iova_tree_remove_gpa(VhostIOVATree *iova_tree, DMAMap map)
> +{
> +    /* Remove the existing mapping from the IOVA->GPA tree */
> +    iova_tree_remove(iova_tree->iova_gpa_map, map);
> +
> +    /* Remove the corresponding mapping from the IOVA->HVA tree */
> +    iova_tree_remove(iova_tree->iova_taddr_map, map);

If we remove it blindly from both trees, we are keeping the bug, isn't it?

I think the remove should receive the "gpa" as a parameter, same as
alloc_gpa. After that, vhost_iova_tree_remove_gpa looks the right iova
into iova_gpa_map. And only after that, it removes that iova from
iova_tree_remove.

If it makes things easier it could receive (hwaddr gpa, size_t len) or
all of the info in a DMAMap. What do you think?

> +}
> diff --git a/hw/virtio/vhost-iova-tree.h b/hw/virtio/vhost-iova-tree.h
> index 4adfd79ff0..511c6d18ae 100644
> --- a/hw/virtio/vhost-iova-tree.h
> +++ b/hw/virtio/vhost-iova-tree.h
> @@ -23,5 +23,10 @@ const DMAMap *vhost_iova_tree_find_iova(const VhostIOVATree *iova_tree,
>                                          const DMAMap *map);
>  int vhost_iova_tree_map_alloc(VhostIOVATree *iova_tree, DMAMap *map);
>  void vhost_iova_tree_remove(VhostIOVATree *iova_tree, DMAMap map);
> +const DMAMap *vhost_iova_gpa_tree_find_iova(const VhostIOVATree *iova_tree,
> +                                            const DMAMap *map);
> +int vhost_iova_tree_map_alloc_gpa(VhostIOVATree *iova_tree, DMAMap *map,
> +                                  hwaddr gpa);
> +void vhost_iova_tree_remove_gpa(VhostIOVATree *iova_tree, DMAMap map);
>
>  #endif
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 3cdaa12ed5..591ff426e7 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -365,9 +365,16 @@ static void vhost_vdpa_listener_region_add(MemoryListener *listener,
>          mem_region.size = int128_get64(llsize) - 1,
>          mem_region.perm = IOMMU_ACCESS_FLAG(true, section->readonly),
>
> -        r = vhost_iova_tree_map_alloc(s->iova_tree, &mem_region);
> +        r = vhost_iova_tree_map_alloc_gpa(s->iova_tree, &mem_region,
> +                                          section->offset_within_address_space);
>          if (unlikely(r != IOVA_OK)) {
>              error_report("Can't allocate a mapping (%d)", r);
> +
> +            /* Insertion to IOVA->GPA tree failed */
> +            if (mem_region.translated_addr ==
> +                section->offset_within_address_space) {
> +                goto fail_map;
> +            }

We can move this cleanup code into vhost_iova_tree_map_alloc_gpa, isn't it?

>              goto fail;
>          }
>
> @@ -386,7 +393,7 @@ static void vhost_vdpa_listener_region_add(MemoryListener *listener,
>
>  fail_map:
>      if (s->shadow_data) {
> -        vhost_iova_tree_remove(s->iova_tree, mem_region);
> +        vhost_iova_tree_remove_gpa(s->iova_tree, mem_region);
>      }
>
>  fail:
> @@ -440,21 +447,18 @@ static void vhost_vdpa_listener_region_del(MemoryListener *listener,
>
>      if (s->shadow_data) {
>          const DMAMap *result;
> -        const void *vaddr = memory_region_get_ram_ptr(section->mr) +
> -            section->offset_within_region +
> -            (iova - section->offset_within_address_space);
>          DMAMap mem_region = {
> -            .translated_addr = (hwaddr)(uintptr_t)vaddr,
> +            .translated_addr = section->offset_within_address_space,
>              .size = int128_get64(llsize) - 1,
>          };
>
> -        result = vhost_iova_tree_find_iova(s->iova_tree, &mem_region);
> +        result = vhost_iova_gpa_tree_find_iova(s->iova_tree, &mem_region);
>          if (!result) {
>              /* The memory listener map wasn't mapped */
>              return;
>          }
>          iova = result->iova;
> -        vhost_iova_tree_remove(s->iova_tree, *result);
> +        vhost_iova_tree_remove_gpa(s->iova_tree, *result);
>      }
>      vhost_vdpa_iotlb_batch_begin_once(s);
>      /*
> --
> 2.43.5
>