Re: [PATCH 2/3] KVM: arm64: Declare support for KVM_CAP_MEMORY_FAULT_INFO

[Oliver Upton <oliver.upton@linux.dev>]

On Fri, Aug 02, 2024 at 10:40:30PM +0000, Anish Moorthy wrote:
> Although arm64 doesn't currently use memory fault exits anywhere,
> it's still valid to advertise the capability: and a subsequent commit
> will add KVM_EXIT_MEMORY_FAULTs to the stage-2 fault handler
> 
> Signed-off-by: Anish Moorthy <amoorthy@google.com>
> ---
>  Documentation/virt/kvm/api.rst | 2 +-
>  arch/arm64/kvm/arm.c           | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 8e5dad80b337..49c504b12688 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -8128,7 +8128,7 @@ unavailable to host or other VMs.
>  7.34 KVM_CAP_MEMORY_FAULT_INFO
>  ------------------------------

<nitpick>

The wording of the cap documentation isn't as relaxed as I'd
anticipated. Perhaps:

  The presence of this capability indicates that KVM_RUN *may* fill
  kvm_run.memory_fault if ...

IOW, userspace is not guaranteed that the structure is filled for every
'memory fault'.

> -:Architectures: x86
> +:Architectures: x86, arm64

nitpick: alphabetize

>  :Returns: Informational only, -EINVAL on direct KVM_ENABLE_CAP.
>  
>  The presence of this capability indicates that KVM_RUN will fill
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index a7ca776b51ec..4121b5a43b9c 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -335,6 +335,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_ARM_SYSTEM_SUSPEND:
>  	case KVM_CAP_IRQFD_RESAMPLE:
>  	case KVM_CAP_COUNTER_OFFSET:
> +	case KVM_CAP_MEMORY_FAULT_INFO:
>  		r = 1;
>  		break;

Please just squash this into the following patch. Introducing the
capability without the implied functionality doesn't make a lot of
sense.

-- 
Thanks,
Oliver