linux-kernel - Re: [RFC v3 PATCH 5/5] x86: check VM

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Message-ID: <20180702133733.GU19043@dhcp22.suse.cz>
Date:   Mon, 2 Jul 2018 15:37:33 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, willy@...radead.org,
        akpm@...ux-foundation.org, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, tglx@...utronix.de,
        hpa@...or.com, linux-mm@...ck.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v3 PATCH 5/5] x86: check VM_DEAD flag in page fault

On Mon 02-07-18 15:33:11, Laurent Dufour wrote:
> 
> 
> On 02/07/2018 14:45, Michal Hocko wrote:
> > On Mon 02-07-18 14:26:09, Laurent Dufour wrote:
> >> On 02/07/2018 14:15, Michal Hocko wrote:
[...]
> >>> We already do have a model for that. Have a look at MMF_UNSTABLE.
> >>
> >> MMF_UNSTABLE is a mm's flag, here this is a VMA's flag which is checked.
> > 
> > Yeah, and we have the VMA ready for all places where we do check the
> > flag. check_stable_address_space can be made to get vma rather than mm.
> 
> Yeah, this would have been more efficient to check that flag at the beginning
> of the page fault handler rather than the end, but this way it will be easier
> to handle the speculative page fault too ;)

The thing is that it doesn't really need to be called earlier. You are
not risking data corruption on file backed mappings.

-- 
Michal Hocko
SUSE Labs