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Message-ID: <20240816124459.GA24323@willie-the-truck>
Date: Fri, 16 Aug 2024 13:45:00 +0100
From: Will Deacon <will@...nel.org>
To: James Clark <james.clark@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, peterz@...radead.org,
Al Grant <al.grant@....com>, Mark Rutland <mark.rutland@....com>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
"Liang, Kan" <kan.liang@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2] drivers/perf: arm_spe: Use perf_allow_kernel() for
permissions
On Wed, Aug 07, 2024 at 04:51:53PM +0100, James Clark wrote:
> For other PMUs, PERF_SAMPLE_PHYS_ADDR requires perf_allow_kernel()
> rather than just perfmon_capable(). Because PMSCR_EL1_PA is another form
> of physical address, make it consistent and use perf_allow_kernel() for
> SPE as well. PMSCR_EL1_PCT and PMSCR_EL1_CX also get the same change.
>
> This improves consistency and indirectly fixes the following error
> message which is misleading because perf_event_paranoid is not taken
> into account by perfmon_capable():
>
> $ perf record -e arm_spe/pa_enable/
>
> Error:
> Access to performance monitoring and observability operations is
> limited. Consider adjusting /proc/sys/kernel/perf_event_paranoid
> setting ...
>
> Suggested-by: Al Grant <al.grant@....com>
> Signed-off-by: James Clark <james.clark@...aro.org>
> ---
> Changes since v1:
>
> * Export perf_allow_kernel() instead of sysctl_perf_event_paranoid
>
> drivers/perf/arm_spe_pmu.c | 9 ++++-----
> include/linux/perf_event.h | 8 +-------
> kernel/events/core.c | 9 +++++++++
> 3 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
> index 9100d82bfabc..3569050f9cf3 100644
> --- a/drivers/perf/arm_spe_pmu.c
> +++ b/drivers/perf/arm_spe_pmu.c
> @@ -41,7 +41,7 @@
>
> /*
> * Cache if the event is allowed to trace Context information.
> - * This allows us to perform the check, i.e, perfmon_capable(),
> + * This allows us to perform the check, i.e, perf_allow_kernel(),
> * in the context of the event owner, once, during the event_init().
> */
> #define SPE_PMU_HW_FLAGS_CX 0x00001
> @@ -50,7 +50,7 @@ static_assert((PERF_EVENT_FLAG_ARCH & SPE_PMU_HW_FLAGS_CX) == SPE_PMU_HW_FLAGS_C
>
> static void set_spe_event_has_cx(struct perf_event *event)
> {
> - if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && perfmon_capable())
> + if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && !perf_allow_kernel(&event->attr))
> event->hw.flags |= SPE_PMU_HW_FLAGS_CX;
The rationale for this change in the commit message is because other
drivers gate PERF_SAMPLE_PHYS_ADDR on perf_allow_kernel(). However,
putting the PID in contextidr doesn't seem to have anything to do with
that...
> }
>
> @@ -745,9 +745,8 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
>
> set_spe_event_has_cx(event);
> reg = arm_spe_event_to_pmscr(event);
> - if (!perfmon_capable() &&
> - (reg & (PMSCR_EL1_PA | PMSCR_EL1_PCT)))
> - return -EACCES;
> + if (reg & (PMSCR_EL1_PA | PMSCR_EL1_PCT))
Similarly here. What does the physical counter have to do with physical
address sampling other than sharing the word "physical"?
Will
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