path: root/arch/x86/kvm/svm/pmu.c
diff options
authorJim Mattson <jmattson@google.com>2022-02-26 15:41:31 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2022-04-02 05:34:45 -0400
commit9b026073db2f1ad0e4d8b61c83316c8497981037 (patch)
treefd650b42fa95ac94a50c93732e9d150df4beae99 /arch/x86/kvm/svm/pmu.c
parent4f4c4a3ee53cc20569158a05f99b6c2d1f9c998a (diff)
KVM: x86/svm: Clear reserved bits written to PerfEvtSeln MSRs
AMD EPYC CPUs never raise a #GP for a WRMSR to a PerfEvtSeln MSR. Some reserved bits are cleared, and some are not. Specifically, on Zen3/Milan, bits 19 and 42 are not cleared. When emulating such a WRMSR, KVM should not synthesize a #GP, regardless of which bits are set. However, undocumented bits should not be passed through to the hardware MSR. So, rather than checking for reserved bits and synthesizing a #GP, just clear the reserved bits. This may seem pedantic, but since KVM currently does not support the "Host/Guest Only" bits (41:40), it is necessary to clear these bits rather than synthesizing #GP, because some popular guests (e.g Linux) will set the "Host Only" bit even on CPUs that don't support EFER.SVME, and they don't expect a #GP. For example, root@Ubuntu1804:~# perf stat -e r26 -a sleep 1 Performance counter stats for 'system wide': 0 r26 1.001070977 seconds time elapsed Feb 23 03:59:58 Ubuntu1804 kernel: [ 405.379957] unchecked MSR access error: WRMSR to 0xc0010200 (tried to write 0x0000020000130026) at rIP: 0xffffffff9b276a28 (native_write_msr+0x8/0x30) Feb 23 03:59:58 Ubuntu1804 kernel: [ 405.379958] Call Trace: Feb 23 03:59:58 Ubuntu1804 kernel: [ 405.379963] amd_pmu_disable_event+0x27/0x90 Fixes: ca724305a2b0 ("KVM: x86/vPMU: Implement AMD vPMU code for KVM") Reported-by: Lotus Fenn <lotusf@google.com> Signed-off-by: Jim Mattson <jmattson@google.com> Reviewed-by: Like Xu <likexu@tencent.com> Reviewed-by: David Dunn <daviddunn@google.com> Message-Id: <20220226234131.2167175-1-jmattson@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/svm/pmu.c')
1 files changed, 3 insertions, 5 deletions
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index e4163f75c11b..24eb935b6f85 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -262,12 +262,10 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
pmc = get_gp_pmc_amd(pmu, msr, PMU_TYPE_EVNTSEL);
if (pmc) {
- if (data == pmc->eventsel)
- return 0;
- if (!(data & pmu->reserved_bits)) {
+ data &= ~pmu->reserved_bits;
+ if (data != pmc->eventsel)
reprogram_gp_counter(pmc, data);
- return 0;
- }
+ return 0;
return 1;