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

[Vitaly Kuznetsov]

Sean Christopherson <sean.j.christopherson@xxxxxxxxx> writes:

> On Tue, Aug 27, 2019 at 09:54:39AM -0700, Jim Mattson wrote:
>> On Tue, Aug 27, 2019 at 9:04 AM Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> 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@xxxxxxxxxx>
>> > ---
>> >  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.
>
> Yep, this will trigger a warning on compilers with -Wimplicit-fallthrough.

I always forget there's more than checkpatch.pl :-) Thanks you your
reviews guys, I'm going to send v2 of this patchset without PATCH1 which
was already queued by Radim.

-- 
Vitaly