linux-kernel - Re: [PATCH v7 05/10] x86/nmi: Assign and register NMI-source vectors

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Message-ID: <a2d0c1ac-eac1-4972-b110-1611d1733d7e@intel.com>
Date: Thu, 10 Jul 2025 17:32:53 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: Xin Li <xin@...or.com>, "H . Peter Anvin" <hpa@...or.com>, Andy Lutomirski
	<luto@...nel.org>, 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>, "Sean
 Christopherson" <seanjc@...gle.com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, "Luck,
 Tony" <tony.luck@...el.com>, "Zhang, Rui" <rui.zhang@...el.com>, "Steven
 Rostedt" <rostedt@...dmis.org>, "andrew.cooper3@...rix.com"
	<andrew.cooper3@...rix.com>, "Kirill A . Shutemov"
	<kirill.shutemov@...ux.intel.com>, Jacob Pan <jacob.pan@...ux.microsoft.com>,
	Andi Kleen <ak@...ux.intel.com>, "Huang, Kai" <kai.huang@...el.com>,
	"Sandipan Das" <sandipan.das@....com>, "linux-perf-users@...r.kernel.org"
	<linux-perf-users@...r.kernel.org>, "linux-edac@...r.kernel.org"
	<linux-edac@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 05/10] x86/nmi: Assign and register NMI-source vectors

On 7/8/2025 12:30 AM, Zhuo, Qiuxu wrote:
>> From: Mehta, Sohil <sohil.mehta@...el.com>
>>
>> We have warnings that should flag any time multiple handlers are registered
>> for SERR or IO_CHK:
>>
>> 	/*
>> 	 * Indicate if there are multiple registrations on the
>> 	 * internal NMI handler call chains (SERR and IO_CHECK).
>> 	 */
>> 	WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
>> 	WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc-
>>> head));
>>
> 
> The warning doesn't imply that it must be a single NMI handler. 
> Otherwise, why not use a single NMI callback pointer per platform NMI 
> type for registration in the current NMI code? 
> 

You are right, the warning doesn't prevent multiple handlers from being
registered. But, it is also impractical that someone ignores a kernel
warning in production.

> I just don't want your comments or commit messages to 
> mismatch the current code as it stands.
> 

Having precise comments is definitely better. I will reword the comment
to say why NMI-source reporting isn't needed in practice for platform NMIs.