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

Commit 1084b1988d (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>
Cc: <stable@vger.kernel.org> # 4.4+
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
This commit is contained in:
Ross Lagerwall 2016-03-17 16:51:59 +00:00 committed by David Vrabel
parent 101ecde566
commit 60901df3ae
1 changed files with 2 additions and 2 deletions
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4
include/xen/page.h
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@ -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)