linux-kernel - Re: [PATCH V5] arm64: perf: Make exporting of pmu events configurable

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Date:   Thu, 9 Jun 2022 16:05:20 +0530
From:   Srinivasarao Pathipati <quic_c_spathi@...cinc.com>
To:     Will Deacon <will@...nel.org>
CC:     <mark.rutland@....com>, <peterz@...radead.org>, <mingo@...hat.com>,
        <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <jolsa@...nel.org>, <namhyung@...nel.org>,
        <catalin.marinas@....com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5] arm64: perf: Make exporting of pmu events configurable

On our Qualcomm platforms, The X bit is getting set by firmware at early 
bootup for Qualcomm use cases
and non-secure world is resetting it, that causing issue.

On 6/9/2022 3:32 PM, Will Deacon wrote:
> On Mon, May 23, 2022 at 05:19:34PM +0530, Srinivasarao Pathipati wrote:
>> The PMU export bit (PMCR_EL0.X) is getting reset during pmu reset,
>> Make is configurable using sysctls to enable/disable at runtime.
>> It can also be enabled at early bootup with kernel arguments.
>>
>> Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@...cinc.com>
>> ---
>> Changes since V4:
>> 	- Registering sysctls dynamically for only arm64 as suggested by Will
>> 	- Not removed the code to configure with kernel parameters
>> 	  as the sysctl's kernel parameter(sysctl.kernel.export_pmu_events)
>> 	  is not working at early bootup. pmu_reset() getting called before
>> 	  sysctl's kernel parameter is set.
> Why do you need this during early bootup? Perf won't program any events
> until much later and if somebody else is configuring the PMU before
> entering Linux then they can also set that X bit in the PMCR.
>
> Will