linux-kernel - RE: [PATCH] iommu/amd: Fix for L2 race with VM invalidation

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Date:	Wed, 14 May 2014 11:38:25 +0000
From:	"Cornwall, Jay" <Jay.Cornwall@....com>
To:	Joerg Roedel <joro@...tes.org>,
	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"Hurwitz, Sherry" <sherry.hurwitz@....com>,
	"Naru, Kim" <Kim.Naru@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] iommu/amd: Fix for L2 race with VM invalidation

Hi,

I'm not sure why you're submitting this, Suravee?

We already agreed that we need the extra mmu_notifier point, proposed by Joerg back in 2011, to eliminate the race. I had thought we were waiting on that to be implemented.

________________________________________
From: Joerg Roedel [joro@...tes.org]
Sent: Wednesday, May 14, 2014 4:29 AM
To: Suthikulpanit, Suravee
Cc: iommu@...ts.linux-foundation.org; Hurwitz, Sherry; Naru, Kim; linux-kernel@...r.kernel.org; Cornwall, Jay
Subject: Re: [PATCH] iommu/amd: Fix for L2 race with VM invalidation

On Wed, May 14, 2014 at 01:34:12AM -0500, suravee.suthikulpanit@....com wrote:
> A low probability race exists with this fix. Translations received
> within the critical section to PTEs which are concurrently being
> invalidated may resolve to stale mappings.

Sorry, no. This patch can cause silent data corruption when the pages in
these stale mappings get reused. I understand that the current way does
not work either and can cause failures in the GPU, but silent data
corruption is worse than that.

How about putting the page-fault requests on hold between
invalidate_range_start/end()? The GPU will not see the failures, just a
longer delay until the page faults are handled.

        Joerg

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