Re: [PATCH 3/3] KVM: x86: announce KVM_CAP_HYPERV_ENLIGHTENED_VMCS support only when it is available

[Jim Mattson <jmattson@google.com>]

On Tue, Aug 27, 2019 at 9:04 AM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> It was discovered that after commit 65efa61dc0d5 ("selftests: kvm: provide
> common function to enable eVMCS") hyperv_cpuid selftest is failing on AMD.
> The reason is that the commit changed _vcpu_ioctl() to vcpu_ioctl() in the
> test and this one can't fail.
>
> Instead of fixing the test is seems to make more sense to not announce
> KVM_CAP_HYPERV_ENLIGHTENED_VMCS support if it is definitely missing
> (on svm and in case kvm_intel.nested=0).
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/kvm/x86.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d1cd0fcff9e7..ef2e8b138300 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3106,7 +3106,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_HYPERV_EVENTFD:
>         case KVM_CAP_HYPERV_TLBFLUSH:
>         case KVM_CAP_HYPERV_SEND_IPI:
> -       case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
>         case KVM_CAP_HYPERV_CPUID:
>         case KVM_CAP_PCI_SEGMENT:
>         case KVM_CAP_DEBUGREGS:
> @@ -3183,6 +3182,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>                 r = kvm_x86_ops->get_nested_state ?
>                         kvm_x86_ops->get_nested_state(NULL, NULL, 0) : 0;
>                 break;
> +       case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
> +               r = kvm_x86_ops->nested_enable_evmcs != NULL;

You should probably have an explicit break here, in case someone later
adds another case below.

>         default:
>                 break;
>         }
> --
> 2.20.1
>