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:
serial8250_console_write+0xfe/0x1f0
call_console_drivers.constprop.0+0x9d/0x120
console_unlock+0x1ea/0x460
Call traces are different but the crash is imminent. The problem was
blindly bisected to the commit
c54086ec378b ("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
c54086ec378b6c708c9c94fb45545554ac9fcda9.
Reported-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <
20200619094046.654019-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>