linux-kernel - Re: [RFC v5 01/11] mm: Dont assume page-table invariance during faults

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Date:   Fri, 07 Jul 2017 17:07:02 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [RFC v5 01/11] mm: Dont assume page-table invariance during
 faults

On Fri, 2017-06-16 at 19:52 +0200, Laurent Dufour wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> One of the side effects of speculating on faults (without holding
> mmap_sem) is that we can race with free_pgtables() and therefore we
> cannot assume the page-tables will stick around.
> 
> Remove the relyance on the pte pointer.
             ^^ reliance

Looking at the changelog and the code the impact is not clear.
It looks like after this patch we always assume the pte is not
the same. What is the impact of this patch?

Balbir Singh.