Re: [Patch v6 09/20] perf/x86/intel: Keep LBR frozen throughout PMI handling

[sashiko-bot@kernel.org]

> For the platforms which has 4+ PMU version, streamline LBR freeze is
> supported. The PERF_GLOBAL_STATUS.LBR_FRZ bit is set to freeze LBR once
> a PMU counter overflow. However, the current PMI handler clears the LBR
> freeze bit too early, allowing branch operations that occur during PMI
> handling to be recorded into the LBR stack.
> 
> This can pollute or overwrite the intended branch snapshot, especially
> when bpf_get_branch_snapshot() is invoked from bpf_overflow_handler().
> In that case, branches recorded while processing the PMI are mixed into
> the original LBR data.
> 
> Defer unfreezing until after PMI handling completes so the LBR remains
> frozen for the entire PMI path and no branch activity from the handler
> is recorded.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://lore.kernel.org/all/sashiko-outbox-179823@kernel.org/
> Fixes: 425507fa5f32 ("perf/x86/intel/lbr: Optimize v4 LBR unfreezing")
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261106043257.842864-1-dapeng1.mi@linux.intel.com?part=9