Re: [PATCH v2 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Apr 21, 2022 at 11:16:59AM +0530, Sandipan Das wrote:
> On some x86 processors, CPUID leaf 0xA provides information
> on Architectural Performance Monitoring features. 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 leaf and the 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 4b62d80bb22f..6bd65cad75ef 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -872,6 +872,11 @@ 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) {

This is the obligatory question about HYGON; should they be included
here?

x86 is getting a number of me-too patches from both sides, where
behaviour has diverged for no raisin and then needs to be fixed up
again.

> +			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> +			break;
> +		}
> +
>  		perf_get_x86_pmu_capability(&cap);
>  
>  		/*
> -- 
> 2.32.0
>