linux-kernel - Re: [PATCH] Revert "mm: always flush VMA ranges affected by zap_page

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Date:   Mon, 16 Jul 2018 14:12:46 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Rik van Riel <riel@...riel.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "kirill.shutemov" <kirill.shutemov@...ux.intel.com>,
        Minchan Kim <minchan@...nel.org>,
        kernel-team <kernel-team@...com>
Subject: Re: [PATCH] Revert "mm: always flush VMA ranges affected by
 zap_page_range"

On Fri, Jul 06, 2018 at 01:10:19PM -0400, Rik van Riel wrote:
> There was a bug in Linux that could cause madvise (and mprotect?)
> system calls to return to userspace without the TLB having been
> flushed for all the pages involved.
> 
> This could happen when multiple threads of a process made simultaneous
> madvise and/or mprotect calls.
> 
> This was noticed in the summer of 2017, at which time two solutions
> were created:
> 56236a59556c ("mm: refactor TLB gathering API")
> 99baac21e458 ("mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem")
> and
> 4647706ebeee ("mm: always flush VMA ranges affected by zap_page_range")
> 
> We need only one of these solutions, and the former appears to be
> a little more efficient than the latter, so revert that one.
> 
> This reverts commit 4647706ebeee6e50f7b9f922b095f4ec94d581c3.
> ---
>  mm/memory.c | 14 +-------------
>  1 file changed, 1 insertion(+), 13 deletions(-)

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs