Messages in this thread | | | Date | Fri, 18 Mar 2022 13:29:11 +0530 | Subject | Re: [PATCH 7/7] kvm: x86/cpuid: Fix Architectural Performance Monitoring support | From | Sandipan Das <> |
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On 3/17/2022 5:37 PM, Peter Zijlstra wrote: > 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.
That's in the works as well. However, in this case, Qemu will have to test CPUID Fn8000_0022 EAX bit 0 to see if the global control and status registers are available.
- Sandipan
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