Date:   Wed, 15 Feb 2023 09:01:25 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Zeng Heng <zengheng4@huawei.com>, mingo@redhat.com, bp@alien8.de,
        jroedel@suse.de, vbabka@suse.cz, hpa@zytor.com, tglx@linutronix.de,
        eric.devolder@oracle.com, tiwai@suse.de, keescook@chromium.org,
        dave.hansen@linux.intel.com, linux-kernel@vger.kernel.org,
        x86@kernel.org, liwei391@huawei.com, xiexiuqi@huawei.com,
        kexec@lists.infradead.org
Subject: Re: [PATCH v3] x86/kdump: Handle blocked NMIs interrupt to avoid
 kdump crashes
Message-ID: <Y+wu5UJTzVIYrsbK@MiWiFi-R3L-srv>
References: <20230202014053.3604176-1-zengheng4@huawei.com>
 <Y9t9wvQ0HRwCs1Xh@hirez.programming.kicks-ass.net>
 <e57ba121-5bcc-e63b-691d-3e3d998e9e48@huawei.com>
 <Y+tZE8ixmlIDYrOu@hirez.programming.kicks-ass.net>
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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.
>