Re: [Patch v5 13/18] perf/x86/intel: Refresh LBR stack for non-PEBS LBR events if needed

[sashiko-bot@kernel.org]

> PEBS and non-PEBS events currently share the same LBR stack,
> cpuc->lbr_stack. In the PMI handler, the non-PEBS path refreshes the
> LBR state before the PEBS buffer is drained.
> 
> When PEBS and non-PEBS LBR events overflow in the same PMI, draining the
> PEBS buffer can overwrite the shared LBR stack with the PEBS snapshot.
> This leaves stale LBR data from the PEBS record in place, and userspace
> may observe the wrong branch stack instead of the live LBR state at PMI
> entry.
> 
> Add a lbr_need_update flag to indicate when the LBR state must be
> refreshed. If PEBS events and non-PEBS LBR events overflow in the same
> PMI, set this flag so the non-PEBS LBR event refreshes the live LBR
> state. Since the LBR state is frozen for the duration of PMI handling, it
> only needs to be read once even when multiple non-PEBS LBR events
> overflow in the same PMI.
> 
> Fixes: c22497f5838c ("perf/x86/intel: Support adaptive PEBS v4")
> 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/20261029043914.1395147-1-dapeng1.mi@linux.intel.com?part=13