linux-kernel - Re: [perf] perf_fuzzer causes unchecked MSR access error

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Date:   Wed, 3 Mar 2021 11:28:39 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [perf] perf_fuzzer causes unchecked MSR access error

On Wed, Mar 3, 2021 at 10:16 AM Vince Weaver <vincent.weaver@...ne.edu> wrote:
>
> Hello
>
> on my Haswell machine the perf_fuzzer managed to trigger this message:
>
> [117248.075892] unchecked MSR access error: WRMSR to 0x3f1 (tried to write 0x0400000000000000) at rIP: 0xffffffff8106e4f4 (native_write_msr+0x4/0x20)
> [117248.089957] Call Trace:
> [117248.092685]  intel_pmu_pebs_enable_all+0x31/0x40
> [117248.097737]  intel_pmu_enable_all+0xa/0x10
> [117248.102210]  __perf_event_task_sched_in+0x2df/0x2f0
> [117248.107511]  finish_task_switch.isra.0+0x15f/0x280
> [117248.112765]  schedule_tail+0xc/0x40
> [117248.116562]  ret_from_fork+0x8/0x30
>
> that shouldn't be possible, should it?  MSR 0x3f1 is MSR_IA32_PEBS_ENABLE
>
Not possible, bit 58 is not defined in PEBS_ENABLE, AFAIK.

>
> this is on recent-git with the patch causing the pebs-related crash
> reverted.
>
> Vince