[Xen-devel] bug in PT write emulation

[John Levon <levon@xxxxxxxxxxxxxxxxx>]

I think the below fix is correct, though as I'm far from comfortable
with this code I'd like some comments first...

'val' is the unmodified pte value written by the guest. We need to use
nl1e instead, which has done the needed PAGE_GLOBAL etc. modifications.

cheers,
john

# HG changeset patch
# User john.levon@xxxxxxx
# Date 1192664022 25200
# Node ID d2eed7e51be31880f04033d1241861602d3628bb
# Parent  a6b52e05bcd026a7d378fff130b90d6eda62209a

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -3204,7 +3204,7 @@ static int ptwr_emulated_update(
         if ( shadow_mode_enabled(d) )
             shadow_lock(d);
         ol1e = l1e_from_intpte(old);
-        if ( cmpxchg((intpte_t *)pl1e, old, val) != old )
+        if ( cmpxchg((intpte_t *)pl1e, old, l1e_get_intpte(nl1e)) != old )
         {
             if ( shadow_mode_enabled(d) )
                 shadow_unlock(d);

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