| Message ID | 20240910175809.2135596-8-david@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | s390x: virtio-mem support | expand |
On 10/09/2024 19.58, David Hildenbrand wrote: > A guest OS that supports memory hotplug / memory devices must during > boot be aware of the maximum possible physical memory address that it might > have to handle at a later stage during its runtime > > For example, the maximum possible memory address might be required to > prepare the kernel virtual address space accordingly (e.g., select page > table hierarchy depth). > > On s390x there is currently no such mechanism that is compatible with > paravirtualized memory devices, because the whole SCLP interface was > designed around the idea of "storage increments" and "standby memory". > Paravirtualized memory devices we want to support, such as virtio-mem, have > no intersection with any of that, but could co-exist with them in the > future if ever needed. > > In particular, a guest OS must never detect and use device memory > without the help of a proper device driver. Device memory must not be > exposed in any firmware-provided memory map (SCLP or diag260 on s390x). > For this reason, these memory devices will be places in memory *above* > the "maximum storage increment" exposed via SCLP. > > Let's provide a new diag500 subcode to query the memory limit determined in > s390_memory_init(). > > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > hw/s390x/s390-hypercall.c | 3 +++ > hw/s390x/s390-hypercall.h | 1 + > 2 files changed, 4 insertions(+) > > diff --git a/hw/s390x/s390-hypercall.c b/hw/s390x/s390-hypercall.c > index f09e8a1d81..ac48fc0961 100644 > --- a/hw/s390x/s390-hypercall.c > +++ b/hw/s390x/s390-hypercall.c > @@ -68,6 +68,9 @@ int handle_diag_500(CPUS390XState *env) > case DIAG500_VIRTIO_CCW_NOTIFY: > env->regs[2] = handle_virtio_ccw_notify(env->regs[2], env->regs[3]); > return 0; > + case DIAG500_STORAGE_LIMIT: > + env->regs[2] = s390_get_memory_limit() - 1; > + return 0; > default: > return -EINVAL; > } > diff --git a/hw/s390x/s390-hypercall.h b/hw/s390x/s390-hypercall.h > index b7ac29f444..f0ca62bcbb 100644 > --- a/hw/s390x/s390-hypercall.h > +++ b/hw/s390x/s390-hypercall.h > @@ -18,6 +18,7 @@ > #define DIAG500_VIRTIO_RESET 1 /* legacy */ > #define DIAG500_VIRTIO_SET_STATUS 2 /* legacy */ > #define DIAG500_VIRTIO_CCW_NOTIFY 3 /* KVM_S390_VIRTIO_CCW_NOTIFY */ > +#define DIAG500_STORAGE_LIMIT 4 > > int handle_diag_500(CPUS390XState *env); Reviewed-by: Thomas Huth <thuth@redhat.com> Sounds very reasonable to me - but it would be good to get an Ack/Reviewed-by from IBM folks here (in case they prefer a different interface)... hope they'll join the discussion! Thomas
On 9/12/24 10:19 AM, Thomas Huth wrote: > On 10/09/2024 19.58, David Hildenbrand wrote: [...] >> diff --git a/hw/s390x/s390-hypercall.h b/hw/s390x/s390-hypercall.h >> index b7ac29f444..f0ca62bcbb 100644 >> --- a/hw/s390x/s390-hypercall.h >> +++ b/hw/s390x/s390-hypercall.h >> @@ -18,6 +18,7 @@ >> #define DIAG500_VIRTIO_RESET 1 /* legacy */ >> #define DIAG500_VIRTIO_SET_STATUS 2 /* legacy */ >> #define DIAG500_VIRTIO_CCW_NOTIFY 3 /* KVM_S390_VIRTIO_CCW_NOTIFY */ >> +#define DIAG500_STORAGE_LIMIT 4 >> >> int handle_diag_500(CPUS390XState *env); > > Reviewed-by: Thomas Huth <thuth@redhat.com> > > Sounds very reasonable to me - but it would be good to get an > Ack/Reviewed-by from IBM folks here (in case they prefer a different > interface)... hope they'll join the discussion! I've publicized the series on the internal channels yesterday. We're aware of the fact that we need to provide review.
diff --git a/hw/s390x/s390-hypercall.c b/hw/s390x/s390-hypercall.c index f09e8a1d81..ac48fc0961 100644 --- a/hw/s390x/s390-hypercall.c +++ b/hw/s390x/s390-hypercall.c @@ -68,6 +68,9 @@ int handle_diag_500(CPUS390XState *env) case DIAG500_VIRTIO_CCW_NOTIFY: env->regs[2] = handle_virtio_ccw_notify(env->regs[2], env->regs[3]); return 0; + case DIAG500_STORAGE_LIMIT: + env->regs[2] = s390_get_memory_limit() - 1; + return 0; default: return -EINVAL; } diff --git a/hw/s390x/s390-hypercall.h b/hw/s390x/s390-hypercall.h index b7ac29f444..f0ca62bcbb 100644 --- a/hw/s390x/s390-hypercall.h +++ b/hw/s390x/s390-hypercall.h @@ -18,6 +18,7 @@ #define DIAG500_VIRTIO_RESET 1 /* legacy */ #define DIAG500_VIRTIO_SET_STATUS 2 /* legacy */ #define DIAG500_VIRTIO_CCW_NOTIFY 3 /* KVM_S390_VIRTIO_CCW_NOTIFY */ +#define DIAG500_STORAGE_LIMIT 4 int handle_diag_500(CPUS390XState *env);
A guest OS that supports memory hotplug / memory devices must during boot be aware of the maximum possible physical memory address that it might have to handle at a later stage during its runtime For example, the maximum possible memory address might be required to prepare the kernel virtual address space accordingly (e.g., select page table hierarchy depth). On s390x there is currently no such mechanism that is compatible with paravirtualized memory devices, because the whole SCLP interface was designed around the idea of "storage increments" and "standby memory". Paravirtualized memory devices we want to support, such as virtio-mem, have no intersection with any of that, but could co-exist with them in the future if ever needed. In particular, a guest OS must never detect and use device memory without the help of a proper device driver. Device memory must not be exposed in any firmware-provided memory map (SCLP or diag260 on s390x). For this reason, these memory devices will be places in memory *above* the "maximum storage increment" exposed via SCLP. Let's provide a new diag500 subcode to query the memory limit determined in s390_memory_init(). Signed-off-by: David Hildenbrand <david@redhat.com> --- hw/s390x/s390-hypercall.c | 3 +++ hw/s390x/s390-hypercall.h | 1 + 2 files changed, 4 insertions(+)