linux-kernel - Re: [Patch v2 15/24] perf/x86/intel: Add SSP register support for arch-PEBS

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Message-ID: <20250225115450.GO11590@noisy.programming.kicks-ass.net>
Date: Tue, 25 Feb 2025 12:54:50 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [Patch v2 15/24] perf/x86/intel: Add SSP register support for
 arch-PEBS

On Tue, Feb 18, 2025 at 03:28:09PM +0000, Dapeng Mi wrote:

> @@ -651,6 +651,16 @@ int x86_pmu_hw_config(struct perf_event *event)
>  			return -EINVAL;
>  	}
>  
> +	/* sample_regs_user never support SSP register. */
> +	if (unlikely(event->attr.sample_regs_user & BIT_ULL(PERF_REG_X86_SSP)))
> +		return -EINVAL;

We can easily enough read user SSP, no?

Should be possible even on todays machines; MSR_IA32_PL3_SSP provides.