[tip: perf/urgent] perf/x86/intel: Ensure KVM guest PEBS path doesn't set unwanted PERF_GLOBAL_CTRL bits

[tip-bot2 for Sean Christopherson]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     cec38d5c098a350dcf084d345025136ade7e6d1e
Gitweb:        https://git.kernel.org/tip/cec38d5c098a350dcf084d345025136ade7e6d1e
Author:        Sean Christopherson <seanjc@xxxxxxxxxx>
AuthorDate:    Mon, 21 Sep 2026 12:14:09 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 22 Sep 2026 11:02:37 +02:00

perf/x86/intel: Ensure KVM guest PEBS path doesn't set unwanted PERF_GLOBAL_CTRL bits

When reinstating PEBS counters into PERF_GLOBAL_CTRL for a KVM guest, mask
the value with perf's desired/original PERF_GLOBAL_CTRL value to ensure
KVM doesn't unintentionally set reserved bits in PERF_GLOBAL_CTRL.  E.g.
if the guest's PEBS_ENABLE value had bit 63, "Enable Precise Store", set,
then using the raw guest PEBS value would propagate bit 63 to the guest's
PERF_GLOBAL_CTRL value (which thankfully would be a failed VM-Entry, not
a VMX Abort).

The only reason this bug isn't reachable is because KVM doesn't support
"Enable Precise Store" (which is probably a KVM bug?), i.e. bit 63 can't
be set in kvm_pmu->pebs_enable and thus not in arr[pebs_enable].guest.  In
other words, this _should_ be a glorified NOP in the current code base.

Fixes: c59a1f106f5c ("KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260921191418.950933-2-seanjc@xxxxxxxxxx
---
 arch/x86/events/intel/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 1ac2ca3..0400b51 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -5359,7 +5359,7 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr, void *data)
 		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;
+		arr[global_ctrl].guest |= intel_ctrl & arr[pebs_enable].guest;
 	}
 
 	return arr;