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| author | Jim Mattson <jmattson@google.com> | 2022-02-27 02:41:31 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-13 21:59:00 +0300 |
| commit | e7bab9898249ee21c46a722ae8e3c67f1712573a (patch) | |
| tree | c9b872eb5c560c15b4c6df31f0132c6183e94aeb /arch/x86/kvm | |
| parent | 5483640f8efbe4a9f42361935633572b9b925436 (diff) | |
| download | linux-e7bab9898249ee21c46a722ae8e3c67f1712573a.tar.xz | |
KVM: x86/svm: Clear reserved bits written to PerfEvtSeln MSRs
[ 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>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/svm/pmu.c | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c index 369164368819..3faf1d9c6c91 100644 --- a/arch/x86/kvm/svm/pmu.c +++ b/arch/x86/kvm/svm/pmu.c @@ -261,12 +261,10 @@ 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; |