linux-kernel - Re: [perf] fuzzer triggers unchecked MSR access error: WRMSR to 0x318

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Date:   Thu, 29 Jul 2021 12:54:20 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        linux-kernel@...r.kernel.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@...el.com>
Subject: Re: [perf] fuzzer triggers unchecked MSR access error: WRMSR to
 0x318

On Thu, 29 Jul 2021, Peter Zijlstra wrote:

> On Wed, Jul 28, 2021 at 12:49:43PM -0400, Vince Weaver wrote:
> > [32694.087403] unchecked MSR access error: WRMSR to 0x318 (tried to write 0x0000000000000000) at rIP: 0xffffffff8106f854 (native_write_msr+0x4/0x20)
> > [32694.101374] Call Trace:
> > [32694.103974]  perf_clear_dirty_counters+0x86/0x100
> 
> Hmm.. if I read this right that's MSR_ARCH_PERFMON_FIXED_CTR0 + i, given
> that FIXED_CTR0 is 0x309 that gives i == 15, which is FIXED_BTS.
> 
> I'm thinking something like this ought to cure things.

I know it sounds like the complete fix is a bit different from this, but I 
did want to report that the patch does fix the issue on my machine.

Vince Weaver
vincent.weaver@...ne.edu