From: Roger Pau Monné <roger.pau@citrix.com>
Date: Tue, 3 Nov 2015 16:34:09 +0000 (+0000)
Subject: xen-blkback: only read request operation from shared ring once
X-Git-Tag: v3.2.76~48
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c25a100a2e2bf4ca34864f8123bf41e471addc49;p=pandora-kernel.git

xen-blkback: only read request operation from shared ring once

commit 1f13d75ccb806260079e0679d55d9253e370ec8a upstream.

A compiler may load a switch statement value multiple times, which could
be bad when the value is in memory shared with the frontend.

When converting a non-native request to a native one, ensure that
src->operation is only loaded once by using READ_ONCE().

This is part of XSA155.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[bwh: Backported to 3.2:
 - s/READ_ONCE/ACCESS_ONCE/
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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