linux-kernel - Re: [PATCH] x86,tlb: update mm

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Message-ID: <4f7d5752-41eb-4828-8bd8-9bd07e89f4f0@intel.com>
Date: Fri, 8 Nov 2024 12:03:10 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Rik van Riel <riel@...riel.com>, Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
 kernel-team@...a.com
Subject: Re: [PATCH] x86,tlb: update mm_cpumask lazily

On 11/8/24 11:31, Rik van Riel wrote:
>  		/* Start receiving IPIs and then read tlb_gen (and LAM below) */
> -		if (next != &init_mm)
> +		if (next != &init_mm && !cpumask_test_cpu(cpu, mm_cpumask(next)))
>  			cpumask_set_cpu(cpu, mm_cpumask(next));
>  		next_tlb_gen = atomic64_read(&next->context.tlb_gen);

If we're worried about contention on mm_cpumask(), then this hunk makes
sense independently of the lazy updating. We might want to take this
hunk forward before we do the rest because this seems like a no-brainer.