linux-kernel - Re: [PATCH] mm/autonuma: don't use set_pte

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Message-Id: <20170214160514.40765dfab42491b8b7b9bf3c@linux-foundation.org>
Date:   Tue, 14 Feb 2017 16:05:14 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     Rik van Riel <riel@...riel.com>,
        Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/autonuma: don't use set_pte_at when updating
 protnone ptes

On Tue, 14 Feb 2017 19:41:17 +0530 "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:

> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:
> 
> > Architectures like ppc64, use privilege access bit to mark pte non accessible.
> > This implies that kernel can do a copy_to_user to an address marked for numa fault.
> > This also implies that there can be a parallel hardware update for the pte.
> > set_pte_at cannot be used in such scenarios. Hence switch the pte
> > update to use ptep_get_and_clear and set_pte_at combination.
> >
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> 
> With this and other patches a kvm guest is giving me
> 
> ...
> 
> Reverting this patch gets rid of the above hang. But I am running into segfault
> with systemd in guest. It could be some other patches in my local tree.
> 
> Maybe we should hold merging this to 4.11 and wait for this to get more
> testing ?

Shall do.  Please let me know the outcome...