tree 4f74cec939084816caf4056097f0b382ea413ad5
parent 2c185687ab016954557aac80074f5d7f7f5d275c
author Juergen Gross <jgross@suse.com> 1413544566 +0200
committer David Vrabel <david.vrabel@citrix.com> 1414077842 +0100

x86/xen: avoid race in p2m handling

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.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>