Very-Pre-Stable 3.19: [PATCH] xen: correct bug in p2m list initialization

[Stefan Bader]

Just was added to the push-to-linus branch for xen...


-------- Forwarded Message --------
Subject: [PATCH] xen: correct bug in p2m list initialization
Date: Fri, 27 Feb 2015 15:45:29 +0100
From: Juergen Gross <jgross at suse.com>
To: linux-kernel at vger.kernel.org, xen-devel at lists.xensource.com,
konrad.wilk at oracle.com, david.vrabel at citrix.com, boris.ostrovsky at oracle.com,
stefan.bader at canonical.com
CC: Juergen Gross <jgross at suse.com>, stable at vger.kernel.org.#.3.19

Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to
linear virtual mapped sparse p2m list") introduced an error.

During initialization of the p2m list a p2m identity area mapped by
a complete identity pmd entry has to be split up into smaller chunks
sometimes, if a non-identity pfn is introduced in this area.

If this non-identity pfn is not at index 0 of a p2m page the new
p2m page needed is initialized with wrong identity entries, as the
identity pfns don't start with the value corresponding to index 0,
but with the initial non-identity pfn. This results in weird wrong
mappings.

Correct the wrong initialization by starting with the correct pfn.

Cc: stable at vger.kernel.org # 3.19
Reported-by: Stefan Bader <stefan.bader at canonical.com>
Signed-off-by: Juergen Gross <jgross at suse.com>
Tested-by: Stefan Bader <stefan.bader at canonical.com>
---
 arch/x86/xen/p2m.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 740ae30..9f93af5 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -563,7 +563,7 @@ static bool alloc_p2m(unsigned long pfn)
 		if (p2m_pfn == PFN_DOWN(__pa(p2m_missing)))
 			p2m_init(p2m);
 		else
-			p2m_init_identity(p2m, pfn);
+			p2m_init_identity(p2m, pfn & ~(P2M_PER_PAGE - 1));

 		spin_lock_irqsave(&p2m_update_lock, flags);

-- 
2.1.4




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