[PATCH v4 10/10] perf/x86/intel: Check only PMC bits in PEBS_ENABLED when detecting host PEBS usage

[Sean Christopherson]

When checking to see if guest PEBS usage should be disabled due to host
PEBS usage, filter out non-counter bits in PEBS_ENABLE to avoid getting
false positives in the unlikely scenario that "Enable Precise Store" is
enabled without PEBS actually being active for any PMCs.

Note, the other "hidden" usage of pebs_mask is already explicitly masked
with intel_ctrl:

  .guest = intel_ctrl & ~cpuc->intel_ctrl_exclude_guest_mask & ~pebs_mask,

I.e. removing the non-counter bits from pebs_mask doesn't change the value
that is loaded into arr[global_ctrl].guest.

Fixes: 854250329c02 ("KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations")
Suggested-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Reported-by: Sashiko Bot <sashiko-bot@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/20260508234018.F06AEC2BCB0@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/events/intel/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index d9315bb2f221..1ff0586c7b71 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -5323,7 +5323,7 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr,
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 	struct perf_guest_switch_msr *arr = cpuc->guest_switch_msrs;
 	u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
-	u64 pebs_mask = cpuc->pebs_enabled & x86_pmu.pebs_capable;
+	u64 pebs_mask = intel_ctrl & cpuc->pebs_enabled & x86_pmu.pebs_capable;
 	u64 guest_pebs_mask;
 	int global_ctrl;
 
@@ -5375,7 +5375,7 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr,
 	 * the guest wants to use for PEBS, (c) are not excluded from counting
 	 * in the guest, and (d) _are_ excluded from counting in the host.
 	 */
-	guest_pebs_mask = pebs_mask & intel_ctrl & guest_pebs->enable &
+	guest_pebs_mask = pebs_mask & guest_pebs->enable &
 			  ~cpuc->intel_ctrl_exclude_guest_mask &
 			  cpuc->intel_ctrl_exclude_host_mask;
 
-- 
2.55.0.1082.g2b9226bbc0-goog