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From: Will Deacon <will.deacon@arm.com>
To: Jon Masters <jcm@redhat.com>
Cc: peterz@infradead.org, paulmck@linux.vnet.ibm.com,
	kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
	ynorov@caviumnetworks.com, rruigrok@codeaurora.org,
	linux-arch@vger.kernel.org, akpm@linux-foundation.org,
	catalin.marinas@arm.com, timur@codeaurora.org
Subject: Re: [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific pgtable code leading to crashes
Date: Fri, 29 Sep 2017 09:56:34 +0100	[thread overview]
Message-ID: <20170929085634.GA14791@arm.com> (raw)
In-Reply-To: <9f351432-3c6b-3b06-7b49-bc9a5806aff5@redhat.com>

[+ Timur]

On Thu, Sep 28, 2017 at 03:38:00PM -0400, Jon Masters wrote:
> 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.

Yeah, of course. I already posted a point diff to Yury in the original
thread:

http://lists.infradead.org/pipermail/linux-arm-kernel/2017-September/533299.html

so I'd like to queue that as an arm64 fix after we've worked out the general
direction of the full fix. I also don't see why other architectures
(including x86) can't be hit by this, so an alternative (completely
untested) approach would just be to take patch 2 of this series.

The full fix isn't just cosmetic; it's also addressing the wider problem
of unannotated racing page table accesses outside of the specific failure
case we've run into.

Will

  reply	other threads:[~2017-09-29  8:56 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-27 15:49 [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific pgtable code leading to crashes Will Deacon
2017-09-27 15:49 ` [RFC PATCH 1/2] arm64: mm: Use READ_ONCE/WRITE_ONCE when accessing page tables Will Deacon
2017-09-28  8:38   ` Peter Zijlstra
2017-09-28  8:45     ` Will Deacon
2017-09-28 15:43       ` Paul E. McKenney
2017-09-28 15:49         ` Will Deacon
2017-09-28 16:07           ` Paul E. McKenney
2017-09-28 18:59         ` Michael Cree
2017-09-29  0:58           ` Paul E. McKenney
2017-09-29  9:08             ` Will Deacon
2017-09-29 16:29               ` Paul E. McKenney
2017-09-29 16:33                 ` Will Deacon
2017-10-03 19:11                   ` Paul E. McKenney
2017-10-05 16:31                     ` Will Deacon
2017-10-05 16:31                       ` Will Deacon
2017-10-05 16:31                       ` Will Deacon
2017-10-05 19:22                       ` Paul E. McKenney
2017-10-05 19:31                       ` Andrea Parri
2017-10-05 20:09                         ` Paul E. McKenney
2017-09-28 19:18   ` Timur Tabi
2017-09-27 15:49 ` [RFC PATCH 2/2] mm: page_vma_mapped: Ensure pmd is loaded with READ_ONCE outside of lock Will Deacon
2017-09-27 22:01 ` [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific pgtable code leading to crashes Yury Norov
2017-09-28 17:30 ` Richard Ruigrok
2017-09-28 19:38 ` Jon Masters
2017-09-29  8:56   ` Will Deacon [this message]
2017-10-03  6:36     ` Jon Masters
2017-10-05 16:54       ` Will Deacon

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