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perf/x86/core: Completely disable guest PEBS via guest's global_ctrl

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When a guest PEBS counter is cross-mapped by a host counter, software
will remove the corresponding bit in the arr[global_ctrl].guest and
expect hardware to perform a change of state "from enable to disable"
via the msr_slot[] switch during the vmx transaction.

The real world is that if user adjust the counter overflow value small
enough, it still opens a tiny race window for the previously PEBS-enabled
counter to write cross-mapped PEBS records into the guest's PEBS buffer,
when arr[global_ctrl].guest has been prioritised (switch_msr_special stuff)
to switch into the enabled state, while the arr[pebs_enable].guest has not.

Close this window by clearing invalid bits in the arr[global_ctrl].guest.

Fixes: 854250329c ("KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations")
Signed-off-by: Like Xu <likexu@tencent.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220831033524.58561-1-likexu@tencent.com
This commit is contained in:
Like Xu 2022-08-31 11:35:24 +08:00 • committed by Peter Zijlstra
parent 24919fdea6
commit f2aeea5750
1 changed files with 2 additions and 1 deletions
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3
arch/x86/events/intel/core.c
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@ -4061,8 +4061,9 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr, void *data)
/* Disable guest PEBS if host PEBS is enabled. */
arr[pebs_enable].guest = 0;
} else {
/* Disable guest PEBS for cross-mapped PEBS counters. */
/* Disable guest PEBS thoroughly for cross-mapped PEBS counters. */
arr[pebs_enable].guest &= ~kvm_pmu->host_cross_mapped_mask;
arr[global_ctrl].guest &= ~kvm_pmu->host_cross_mapped_mask;
/* Set hw GLOBAL_CTRL bits for PEBS counter when it runs for guest */
arr[global_ctrl].guest |= arr[pebs_enable].guest;
}