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

[ Upstream commit 5a1bde46f98b893cda6122b00e94c0c40a6ead3c ]

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>
Message-Id: <3fef83d9c2b2f7516e8ff50d60851f29a4bcb716.1651058600.git.sandipan.das@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 097eef712cdc0c5692269fb94658a22637924530..0489ffc3dfe5f3b0ad13c56797f8d77641ae67e1 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -532,6 +532,11 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, 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);
 
                /*