linux-kernel - Re: [PATCH v5 2/2] x86/mm: Improve TLB flush documentation

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Message-ID: <20170725100234.qbsuphozotivan3c@hirez.programming.kicks-ass.net>
Date:   Tue, 25 Jul 2017 12:02:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH v5 2/2] x86/mm: Improve TLB flush documentation

On Mon, Jul 24, 2017 at 09:41:39PM -0700, Andy Lutomirski wrote:
> +		/*
> +		 * Resume remote flushes and then read tlb_gen.  The
> +		 * implied barrier in atomic64_read() synchronizes

There is no barrier in atomic64_read().

> +		 * with inc_mm_tlb_gen() like this:
> +		 *
> +		 * switch_mm_irqs_off():	flush request:
> +		 *  cpumask_set_cpu(...);	 inc_mm_tlb_gen();
> +		 *  MB				 MB
> +		 *  atomic64_read(.tlb_gen);	 flush_tlb_others(mm_cpumask());
> +		 */
>  		cpumask_set_cpu(cpu, mm_cpumask(next));
>  		next_tlb_gen = atomic64_read(&next->context.tlb_gen);
>