Commit 49097762 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
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Revert "KVM: VMX: Micro-optimize vmexit time when not exposing PMU"

Guest crashes are observed on a Cascade Lake system when 'perf top' is
launched on the host, e.g.

 BUG: unable to handle kernel paging request at fffffe0000073038
 PGD 7ffa7067 P4D 7ffa7067 PUD 7ffa6067 PMD 7ffa5067 PTE ffffffffff120
 Oops: 0000 [#1] SMP PTI
 CPU: 1 PID: 1 Comm: systemd Not tainted 4.18.0+ #380
 Call Trace:

Call traces are different but the crash is imminent. The problem was
blindly bisected to the commit 041bc42c ("KVM: VMX: Micro-optimize
vmexit time when not exposing PMU"). It was also confirmed that the
issue goes away if PMU is exposed to the guest.

With some instrumentation of the guest we can see what is being switched
(when we do atomic_switch_perf_msrs()):

 vmx_vcpu_run: switching 2 msrs
 vmx_vcpu_run: switching MSR38f guest: 70000000d host: 70000000f
 vmx_vcpu_run: switching MSR3f1 guest: 0 host: 2

The current guess is that PEBS (MSR_IA32_PEBS_ENABLE, 0x3f1) is to blame.
Regardless of whether PMU is exposed to the guest or not, PEBS needs to
be disabled upon switch.

This reverts commit 041bc42c

Reported-by: default avatarMaxime Coquelin <>
Signed-off-by: default avatarVitaly Kuznetsov <>
Message-Id: <>
Signed-off-by: default avatarPaolo Bonzini <>
parent 88c200d9
......@@ -6728,8 +6728,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (vcpu_to_pmu(vcpu)->version)
if (enable_preemption_timer)
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