kvm: x86/cpuid: Only provide CPUID leaf 0xA if host has architectural PMU

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
and Hygon processors. If AMD 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: d89e0112c16d ("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>
Message-Id: <3fef83d9c2b2f7516e8ff50d60851f29a4bcb716.1651058600.git.sandipan.das@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b24ca7f4ed7c8b6603d6d54ec846504c04f0c742..732724ea5b100936ec46639df6e236858a354d7f 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -887,6 +887,11 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
                union cpuid10_eax eax;
                union cpuid10_edx edx;
 
+               if (!static_cpu_has(X86_FEATURE_ARCH_PERFMON)) {
+                       entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+                       break;
+               }
+
                perf_get_x86_pmu_capability(&cap);
 
                /*