linux-kernel - Re: [perf] unchecked MSR access error: WRMSR to 0x3f1

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Message-ID: <c04824b5-5697-1de5-0003-f2c5b73ed006@maine.edu>
Date: Wed, 18 Jun 2025 14:26:04 -0400 (EDT)
From: Vince Weaver <vincent.weaver@...ne.edu>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
cc: Vince Weaver <vincent.weaver@...ne.edu>, linux-kernel@...r.kernel.org, 
    linux-perf-users@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
    Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, 
    Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
    Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
    Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
    Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [perf] unchecked MSR access error: WRMSR to 0x3f1

On Wed, 18 Jun 2025, Liang, Kan wrote:

> No, the error message doesn't say it. Just want to check if you have
> extra information. Because the Topdown perf metrics is only supported on
> p-core. I want to understand whether the code messes up with e-core.

I can't easily tell from the fuzzer as it intentionally switches cores 
often.  I guess I could patch the kernel to report CPU when the WRMSR 
error triggers.

> > I was running just before -rc1.  I've updated to current git but didn't 
> > realize the throttle fix hadn't made it upstream yet so managed to lock up 
> > the machine and not sure when I'll be able to get over to reboot it.
> >
> 
> They are not in rc2 as well. I guess it should be included in rc3.

OK I am running rc2 now (Well, whatever current git is) with the throttle 
fix applied.  The throttle crash is something else, it crashes my test 
machine so hard that even the power button doesn't work, I have to 
physically unplug the machine to reboot it.


> >> - Can this be easily reproduced?
> > 
> > probably.  It's another thing that's a pain to check because it's a 
> > WARN_ONCE I think so I have to reboot in order to see.  Even if it's not 
> > reproducible the fuzzer usually hits it within a few hours.

I am able to reproduce the error on -rc2 using a specific fuzzer random 
seed.  I can possibly try to create a simpler test case but that would be 
a bit of effort.

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