Re: [PATCH] perf/x86/intel: Don't allow extended register sampling for BTS events

[sashiko-bot@kernel.org]

> x86_pmu_hw_config() accepts extended (XMM) register sampling in
> REGS_USER for events without precise_ip, and the same goes for the SIMD
> register fields. The BTS event is such an event, and
> intel_pmu_bts_config() does not reject it.
> 
> For a sample taken in the PMI handler, x86_pmu_update_perf_regs() copies
> the user registers into the per-CPU x86_user_regs, which is a struct
> x86_perf_regs. That is what perf_reg_value() and perf_simd_reg_value()
> expect: they use container_of() on the sampled struct pt_regs to reach
> the fields that follow it.
> 
> intel_pmu_drain_bts_buffer() does not call x86_pmu_update_perf_regs().
> It passes zeroed on-stack registers to perf_prepare_sample(), so the
> generic perf_sample_regs_user() takes the user registers from
> perf_get_regs_user(). That returns task_pt_regs(current), or on x86_64,
> [ ... ]
> patch and its changelog. It has not been reproduced, and the change
> has only been compile-tested.
> 
> Fixes: edd9aec51213 ("perf/x86: Enable XMM register sampling for REGS_USER case")
> Signed-off-by: Jiwoo Kim <arpe1618@gmail.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261114062249.1301-1-arpe1618@gmail.com?part=1