Commit 60901df3 authored Mar 17, 2016 by Ross Lagerwall Committed by David Vrabel Apr 06, 2016

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



Commit 1084b198 (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>

parent 101ecde5

include/xen/page.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -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)

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