linux-kernel - Re: [PATCH v2 1/6] x86/irq: Add enumeration of NMI source reporting CPU feature

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Date: Thu, 27 Jun 2024 16:20:45 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC: X86 Kernel <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, "Thomas
 Gleixner" <tglx@...utronix.de>, Dave Hansen <dave.hansen@...el.com>, "H.
 Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, <linux-perf-users@...r.kernel.org>, Peter Zijlstra
	<peterz@...radead.org>, Andi Kleen <andi.kleen@...el.com>, Xin Li
	<xin3.li@...el.com>
Subject: Re: [PATCH v2 1/6] x86/irq: Add enumeration of NMI source reporting
 CPU feature

On 6/27/2024 3:23 PM, Jacob Pan wrote:

> I don't think this is true. For a simplified example:
> cpuid_deps has the following feature-depends pairs.
> [1, 3]
> [2, 3]
> now, do_clear_cpu_cap(c, 2)
> 
> Before the loop below __set_bit(feature, disable), bit 2 is set. 
> 
> Since there is no other features depend on 2, the loop below will not clear
> any other features. no?
> 

You are right. The table-scan only processes the dependencies of the
feature that is being disabled but not of any other features that might
have a missing dependency.

Maybe it might be useful to have a common function that scans through
all the dependencies at boot. It would mainly help detect hardware (or
VMM) inconsistencies sooner than later.