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

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Message-ID: <Y+wu5UJTzVIYrsbK@MiWiFi-R3L-srv>
Date:   Wed, 15 Feb 2023 09:01:25 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Zeng Heng <zengheng4@...wei.com>, mingo@...hat.com, bp@...en8.de,
        jroedel@...e.de, vbabka@...e.cz, hpa@...or.com, tglx@...utronix.de,
        eric.devolder@...cle.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,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v3] x86/kdump: Handle blocked NMIs interrupt to avoid
 kdump crashes

Add kexec list to CC.

On 02/14/23 at 10:49am, Peter Zijlstra wrote:
> 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?

No, reboot_notifier_list is only handled in kexec reboot/reboot path,
please see kernel_restart_prepare() invocation. Kdump path only shutdown
key component like cpu, interrupt controller.

> 
> If not, someone should look at doing something there.
>