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SubjectRe: [PATCH v2 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA
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Hi Peter,

On 4/26/2022 1:45 PM, Peter Zijlstra wrote:
> 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.
>

From what I understand, Hygon processors also do not support this leaf.
Copying Pu Wen for confirmation.

- Sandipan

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

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