Re: [PATCH 4/6] perf/x86/intel/pt: Clear TraceEn in hardware in cpu_emergency_stop_pt()

[sashiko-bot@kernel.org]

> cpu_emergency_stop_pt() stops tracing through pt_event_stop(), which
> assumes the software state accurately reflects whether tracing is
> enabled.  That assumption can fail when a crash NMI interrupts
> pt_config_start().
> 
> pt_config_start() sets TraceEn in IA32_RTIT_CTL before updating
> event->hw.aux_config.  If a crash NMI arrives in that window,
> pt_config_stop() sees TraceEn clear in aux_config and skips the MSR
> write needed to disable tracing.  Tracing remains active in hardware.
> 
> Alternatively, an earlier NMI in the same window can stop the event
> without restarting it, for example a group throttle calling
> pt_event_stop(event, 0), or a PT PMI for which perf_aux_output_begin()
> fails.  pt_config_stop() again skips the write, so the event is stopped
> only in software: TraceEn remains set in IA32_RTIT_CTL, and
> [ ... ]
> Fixes: 8e105a1fc2a0 ("perf/x86/intel/pt: Factor out pt_config_start()")
> Fixes: 25e8920b301c ("perf/x86/intel/pt: Add sampling support")
> Fixes: 08c7454ceb94 ("perf/x86/intel/pt: Add support for pause / resume")
> Fixes: 2e17bf3a469a ("perf/x86/intel/pt: Fix stop/start with no update")
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261102074039.26983-1-adrian.hunter@intel.com?part=4