linux-kernel - [PATCH 4.9 62/66] kvm: x86/cpuid: Only provide CPUID leaf 0xA if host has architectural PMU

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Message-Id: <20220510130731.583338857@linuxfoundation.org>
Date:   Tue, 10 May 2022 15:07:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vasant Hegde <vasant.hegde@....com>,
        Sandipan Das <sandipan.das@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 62/66] kvm: x86/cpuid: Only provide CPUID leaf 0xA if host has architectural PMU

From: Sandipan Das <sandipan.das@....com>

[ 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@....com>
Signed-off-by: Sandipan Das <sandipan.das@....com>
Message-Id: <3fef83d9c2b2f7516e8ff50d60851f29a4bcb716.1651058600.git.sandipan.das@....com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 a6f8600672d7..c068027ac55f 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -502,6 +502,11 @@ 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);
 
 		/*
-- 
2.35.1