linux-kernel - Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use it in nmi_shootdown

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Message-ID: <7aa93137-4b5e-474f-a99c-47acffdf71a3@redhat.com>
Date: Wed, 4 Dec 2024 12:23:38 -0500
From: Waiman Long <llong@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
 "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use it
 in nmi_shootdown_cpus()

On 12/4/24 8:10 AM, Thomas Gleixner wrote:
> On Tue, Dec 03 2024 at 10:07, Waiman Long wrote:
>> +	/*
>> +	 * Call the emergency handler first, if set
>> +	 * Emergency handler is not traced or checked by nmi_check_duration().
>> +	 */
>> +	ehandler = READ_ONCE(desc->emerg_handler);
>> +	if (ehandler)
>> +		handled = ehandler(type, regs);
> Shouldn't this just stop processing right here?

Yes in the case of crash_nmi_callback(). I suppose it is a no-return 
call. As the emergency handler is supposed to be a general mechanism in 
design, I don't want to make too many assumptions of what will happen 
when the handler is invoked.

What suggested changes do you have in your mind? I do make a minor 
mistake in the functional comment that is reported by kernel test robot 
which I will fix in the next version.

Cheers,
Longman