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    SubjectRe: [PATCH 7/7] kvm: x86/cpuid: Fix Architectural Performance Monitoring support
    On Thu, Mar 17, 2022 at 11:58:36AM +0530, Sandipan Das wrote:
    > CPUID 0xA provides information on Architectural Performance
    > Monitoring features on some x86 processors. It advertises a
    > PMU version which Qemu uses to determine the availability of
    > additional MSRs to manage the PMCs.
    >
    > Upon receiving a KVM_GET_SUPPORTED_CPUID ioctl request for
    > the same, the kernel constructs return values based on the
    > x86_pmu_capability irrespective of the vendor.
    >
    > This CPUID function and additional MSRs are not supported on
    > AMD processors. If PerfMonV2 is detected, the PMU version is
    > set to 2 and guest startup breaks because of an attempt to
    > access a non-existent MSR. Return zeros to avoid this.
    >
    > Fixes: a6c06ed1a60a ("KVM: Expose the architectural performance monitoring CPUID leaf")
    > Reported-by: Vasant Hegde <vasant.hegde@amd.com>
    > Signed-off-by: Sandipan Das <sandipan.das@amd.com>
    > ---
    > arch/x86/kvm/cpuid.c | 5 +++++
    > 1 file changed, 5 insertions(+)
    >
    > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
    > index b8f8d268d058..1d9ca5726167 100644
    > --- a/arch/x86/kvm/cpuid.c
    > +++ b/arch/x86/kvm/cpuid.c
    > @@ -865,6 +865,11 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
    > union cpuid10_eax eax;
    > union cpuid10_edx edx;
    >
    > + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
    > + entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
    > + break;
    > + }
    > +

    Because actually implementing perfmon-v2 would've been too convenient,
    right? IIRC you're very close to actually supporing perfmon-v2
    capability wise here.

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