linux-kernel - Re: [PATCH v3] x86/kdump: Handle blocked NMIs interrupt to avoid kdump crashes

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Date:   Tue, 14 Feb 2023 10:49:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zeng Heng <zengheng4@...wei.com>
Cc:     mingo@...hat.com, bp@...en8.de, jroedel@...e.de, vbabka@...e.cz,
        hpa@...or.com, tglx@...utronix.de, eric.devolder@...cle.com,
        bhe@...hat.com, tiwai@...e.de, keescook@...omium.org,
        dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, liwei391@...wei.com, xiexiuqi@...wei.com
Subject: Re: [PATCH v3] x86/kdump: Handle blocked NMIs interrupt to avoid
 kdump crashes

On Tue, Feb 14, 2023 at 05:30:46PM +0800, Zeng Heng wrote:

> > I never remember the shutdown paths -- do we force wipe the PMU
> > registers somewhere before this?
> 
> I have checked the panic process, and there is no wipe operation for PMU
> registers,
> 
> which causes the watchdog bites.
> 
> Do you mean we should directly disable PMU registers instead of calling
> `iret_to_self` to
> 
> consume blocked NMI interrupts ?

If you don't wipe the PMU, there will be many and continuous NMIs, a
single IRET-to-SELF isn't going to safe you.

Anyway, I had a bit of a grep around and I find we have:

  kernel/events/core.c:   register_reboot_notifier(&perf_reboot_notifier);

which should end up killing all the PMU activity. Somewhere around there
there's also a CONFIG_KEXEC_CORE ifdef, so I'm thinking it gets called
on the panic->crash-kernel path too?

If not, someone should look at doing something there.