linux-kernel - Re: [Xen-devel] [PATCH V2] xen: avoid race in p2m handling

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Message-ID: <54410D06.3010109@citrix.com>
Date:	Fri, 17 Oct 2014 13:35:18 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<david.vrabel@...rix.com>
Subject: Re: [Xen-devel] [PATCH V2] xen: avoid race in p2m handling

On 17/10/14 12:16, Juergen Gross wrote:
> When a new p2m leaf is allocated this leaf is linked into the p2m tree
> via cmpxchg. Unfortunately the compare value for checking the success
> of the update is read after checking for the need of a new leaf. It is
> possible that a new leaf has been linked into the tree concurrently
> in between. This could lead to a leaked memory page and to the loss of
> some p2m entries.
> 
> Avoid the race by using the read compare value for checking the need
> of a new p2m leaf and use ACCESS_ONCE() to get it.
> 
> There are other places which seem to need ACCESS_ONCE() to ensure
> proper operation. Change them accordingly.

Applied, thanks.

David
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