linux-kernel - Re: [PATCH v6 4/9] x86/nmi: Assign and register NMI-source vectors

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Message-ID: <56a641ac-5433-4edd-9552-b31f4cc9d591@intel.com>
Date: Tue, 3 Jun 2025 14:45:47 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Xin Li <xin@...or.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>
CC: "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>, Adrian Hunter <adrian.hunter@...el.com>, Kan Liang
	<kan.liang@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, Zhang Rui
	<rui.zhang@...el.com>, Steven Rostedt <rostedt@...dmis.org>, Andrew Cooper
	<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>, Kai Huang <kai.huang@...el.com>, "Sandipan
 Das" <sandipan.das@....com>, <linux-perf-users@...r.kernel.org>,
	<linux-edac@...r.kernel.org>, <kvm@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 4/9] x86/nmi: Assign and register NMI-source vectors

On 6/3/2025 9:34 AM, Xin Li wrote:
> On 5/13/2025 1:37 PM, Sohil Mehta wrote:
>> Prior to NMI-source support, the vector information was ignored by the
>> hardware while delivering NMIs. With NMI-source, the architecture
>> currently supports a 16-bit source bitmap to identify the source of the
>> NMI. Upon receiving an NMI, this bitmap is delivered as part of the FRED
>> event delivery mechanism to the kernel.
>>
>> Assign a vector space of 0-15 that is specific to NMI-source and
>> independent of the IDT vector space of 0-255. Being a bitmap, the
>> NMI-source vectors do not have any inherent priority associated with
>> them. The order of executing the NMI handlers is up to the kernel.
> 
> I'm thinking should we mention that the bitmap could be extended more
> than 16 bits in future?  Or we just don't emphasize 16-bit or 0~15?
> 

That was mainly to justify the value of NMIS_VECTORS_MAX defined in this
patch. I will include a sentence to mention that the bitmap size could
be extended in the future.

We could even set NMIS_VECTORS_MAX to 64 right now to make this
future-proof. Though in practice, I don't see it happening any time soon.

Sohil