linux-kernel - Re: [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific pgtable code leading to crashes

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Message-ID: <9f351432-3c6b-3b06-7b49-bc9a5806aff5@redhat.com>
Date:   Thu, 28 Sep 2017 15:38:00 -0400
From:   Jon Masters <jcm@...hat.com>
To:     Will Deacon <will.deacon@....com>, peterz@...radead.org,
        paulmck@...ux.vnet.ibm.com, kirill.shutemov@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, ynorov@...iumnetworks.com,
        rruigrok@...eaurora.org, linux-arch@...r.kernel.org,
        akpm@...ux-foundation.org, catalin.marinas@....com
Subject: Re: [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific
 pgtable code leading to crashes

On 09/27/2017 11:49 AM, Will Deacon wrote:

> The moral of the story is that read-after-read (same address) ordering *only*
> applies if READ_ONCE is used consistently. This means we need to fix page
> table dereferences in the core code as well as the arch code to avoid this
> problem. The two RFC patches in this series fix arm64 (which is a bigger fix
> that necessary since I clean things up too) and page_vma_mapped_walk.
> 
> Comments welcome.

Thanks for this Will. I'll echo Timur's comment that it would be ideal
to split this up into the critical piece needed for ordering
access/update to the PMD in the face of a THP split and separately have
the cosmetic cleanups. Needless to say, we've got a bunch of people who
are tracking this one and tracking it ready for backport. We just got
THP re-enabled so I'm pretty keen that we not have to disable again.

Jon.

-- 
Computer Architect | Sent from my Fedora powered laptop