CVE-2026-97960

In the Linux kernel, the following vulnerability has been resolved:

perf/x86/intel: Prevent drain_pebs() reentry

The PEBS buffer is shared by all events on a CPU, so drain_pebs() must
not be reentered. If so, one instance may observe stale buffer state and
potentially access out-of-bound memory.

Most invocations happen in NMI context, which naturally prevents reentry.
However, drain_pebs() is also reachable from process context via
intel_pmu_drain_pebs_buffer().

In those paths, the PMU is often already disabled, but not guaranteed.
For example, __intel_pmu_pebs_disable() only disables the target counter,
so other active counters can still raise a PMI and interrupt an in-flight
drain_pebs(). Here is an example,

__perf_addr_filters_adjust()
  perf_event_stop()
    __perf_event_stop()
      x86_pmu_stop() (event->pmu->stop)
        intel_pmu_disable_event()
          intel_pmu_pebs_disable()
            __intel_pmu_pebs_disable()
              intel_pmu_drain_large_pebs()
                intel_pmu_drain_pebs_buffer()

Introduce __intel_pmu_quiesce() and __intel_pmu_resume() helpers and
use them in intel_pmu_drain_large_pebs() to disable the full PMU
around the intel_pmu_drain_pebs_buffer() call, preventing reentry.

Also add a warning in intel_pmu_drain_pebs_buffer() when the full PMU is
not disabled.