Date:   Tue, 14 Feb 2023 10:49:07 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Zeng Heng <zengheng4@huawei.com>
Cc:     mingo@redhat.com, bp@alien8.de, jroedel@suse.de, vbabka@suse.cz,
        hpa@zytor.com, tglx@linutronix.de, eric.devolder@oracle.com,
        bhe@redhat.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
Subject: Re: [PATCH v3] x86/kdump: Handle blocked NMIs interrupt to avoid
 kdump crashes
Message-ID: <Y+tZE8ixmlIDYrOu@hirez.programming.kicks-ass.net>
References: <20230202014053.3604176-1-zengheng4@huawei.com>
 <Y9t9wvQ0HRwCs1Xh@hirez.programming.kicks-ass.net>
 <e57ba121-5bcc-e63b-691d-3e3d998e9e48@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <e57ba121-5bcc-e63b-691d-3e3d998e9e48@huawei.com>
Precedence: bulk

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.