[Xen-changelog] Fix emulated writable pagetable updates where access is

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 0cd6a23b8d6e0ccf91f48b0a93aa804faf655db9
# Parent  67a13c0ac87d7878444a5ace1844f4bfb4769295
Fix emulated writable pagetable updates where access is
less than a full pte and operation requires cmpxchg.

Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

diff -r 67a13c0ac87d -r 0cd6a23b8d6e xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Thu Aug 18 17:46:26 2005
+++ b/xen/arch/x86/mm.c Thu Aug 18 18:02:46 2005
@@ -3059,7 +3059,7 @@
     }
 
     /* Turn a sub-word access into a full-word access. */
-    if (bytes != sizeof(physaddr_t))
+    if ( bytes != sizeof(physaddr_t) )
     {
         int           rc;
         physaddr_t    full;
@@ -3076,6 +3076,10 @@
         val  &= (((physaddr_t)1 << (bytes*8)) - 1);
         val <<= (offset)*8;
         val  |= full;
+        /* Also fill in missing parts of the cmpxchg old value. */
+        old  &= (((physaddr_t)1 << (bytes*8)) - 1);
+        old <<= (offset)*8;
+        old  |= full;
     }
 
     /* Read the PTE that maps the page being updated. */

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