Patch "xen: Fix page <-> pfn conversion on 32 bit systems" has been added to the 4.4-stable tree

Patch "xen: Fix page <-> pfn conversion on 32 bit systems" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    xen: Fix page <-> pfn conversion on 32 bit systems

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xen-fix-page-pfn-conversion-on-32-bit-systems.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 60901df3aed230d4565dca003f11b6a95fbf30d9 Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <ross.lagerwall@citrix.com>
Date: Thu, 17 Mar 2016 16:51:59 +0000
Subject: xen: Fix page <-> pfn conversion on 32 bit systems

From: Ross Lagerwall <ross.lagerwall@citrix.com>

commit 60901df3aed230d4565dca003f11b6a95fbf30d9 upstream.

Commit 1084b1988d22dc165c9dbbc2b0e057f9248ac4db (xen: Add Xen specific
page definition) caused a regression in 4.4.

The xen functions to convert between pages and pfns fail due to an
overflow on systems where a physical address may not fit in an
unsigned long (e.g. x86 32 bit PAE systems). Rework the conversion to
avoid overflow. This should also result in simpler object code.

This bug manifested itself as disk corruption with Linux 4.4 when
using blkfront in a Xen HVM x86 32 bit guest with more than 4 GiB of
memory.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/xen/page.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/include/xen/page.h
+++ b/include/xen/page.h
@@ -15,9 +15,9 @@
  */
 
 #define xen_pfn_to_page(xen_pfn)	\
-	((pfn_to_page(((unsigned long)(xen_pfn) << XEN_PAGE_SHIFT) >> PAGE_SHIFT)))
+	(pfn_to_page((unsigned long)(xen_pfn) >> (PAGE_SHIFT - XEN_PAGE_SHIFT)))
 #define page_to_xen_pfn(page)		\
-	(((page_to_pfn(page)) << PAGE_SHIFT) >> XEN_PAGE_SHIFT)
+	((page_to_pfn(page)) << (PAGE_SHIFT - XEN_PAGE_SHIFT))
 
 #define XEN_PFN_PER_PAGE	(PAGE_SIZE / XEN_PAGE_SIZE)
 


Patches currently in stable-queue which might be from ross.lagerwall@citrix.com are

queue-4.4/xen-balloon-fix-crash-when-ballooning-on-x86-32-bit-pae.patch
queue-4.4/xen-fix-page-pfn-conversion-on-32-bit-systems.patch