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

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Date:	Wed, 14 May 2014 11:29:21 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	suravee.suthikulpanit@....com
Cc:	iommu@...ts.linux-foundation.org, sherry.hurwitz@....com,
	kim.naru@....com, linux-kernel@...r.kernel.org,
	Jay Cornwall <jay.cornwall@....com>
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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