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

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: 854250329c02 ("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

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index e8eb936..c20d8cd 100644 (file)
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -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;
        }