From: Jim Mattson jmattson@google.com
[ Upstream commit 9b026073db2f1ad0e4d8b61c83316c8497981037 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kvm/svm/pmu.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c index 04e483471dbb..39ee0e271d9c 100644 --- a/arch/x86/kvm/svm/pmu.c +++ b/arch/x86/kvm/svm/pmu.c @@ -260,12 +260,10 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) /* MSR_EVNTSELn */ 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;