[PATCH 7/7] kvm: x86/cpuid: Fix Architectural Performance Monitoring support

[Sandipan Das <sandipan.das@amd.com>]

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;
+		}
+
 		perf_get_x86_pmu_capability(&cap);
 
 		/*
-- 
2.32.0