linux-kernel - Re: [PATCH 2/2] x86/mm: clarify "prev" usage in switch_mm_irqs

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Date: Thu, 22 Feb 2024 10:47:03 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/mm: clarify "prev" usage in switch_mm_irqs_off()

On 2/22/24 10:43, Yosry Ahmed wrote:
>> /*
>>  * This optimizes when not actually switching mm's.  Some architectures
>>  * use the 'unused' argument for this optimization, but x86 must use
>>  * 'cpu_tlbstate.loaded_mm' instead because it does not always keep
>>  * ->active_mm up to date.
>>  */
> Yes, this is more clear, thanks! However, Andrew already merged that
> patch into mm-stable, so it cannot be amended. I can send a separate
> patch to rewrite the comment tho if you'd like, WDYT?
> 
>> Also, I think it might be useful to have the rule that arch/x86 code
>> _always_ calls switch_mm_irqs_off() with the first argument (the
>> newly-named 'unused') set to NULL.  I think there's only one site:
> Agreed. I can also send a separate patch for this. Thanks!

That would be great.  I'd be happy to ack them.