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From:   Sandipan Das <sandipan.das@amd.com>
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Subject: [PATCH v4 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA
Date:   Wed, 27 Apr 2022 17:01:49 +0530
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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: 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..e66ebb747084 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 (!static_cpu_has(X86_FEATURE_ARCH_PERFMON)) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+			break;
+		}
+
 		perf_get_x86_pmu_capability(&cap);
 
 		/*
-- 
2.34.1