[PATCH] Allow 32bit PAE guests to change their L3 entries

["Christoph Egger" <Christoph.Egger@amd.com>]

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Hi!

adjust_guest_l3e() adds (_PAGE_USER|_PAGE_RW) to the entry, and then
get_page_from_l3e() checks that _PAGE_USER or _PAGE_RW are not present
for PAE guests.  get_page_from_l3e() will always fail at this point
for PAE guests.

Attached patch fixes this. This bug has been uncovered with NetBSD 32bit PAE 
guests.

Patch from Manuel Bouyer <bouyer@netbsd.org> for xen-3.1-testing,
ported to xen-unstable by me.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>


Keir: Please apply this patch also to xen-3.2-testing and xen-3.1-testing.



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diff -r 819399d0bdb1 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c	Fri Feb 15 14:16:42 2008 +0000
+++ b/xen/arch/x86/mm.c	Mon Feb 18 10:55:18 2008 +0100
@@ -1567,14 +1567,14 @@ static int mod_l3_entry(l3_pgentry_t *pl
             return 0;
         }
 
-        adjust_guest_l3e(nl3e, d);
-
         /* Fast path for identical mapping and presence. */
         if (!l3e_has_changed(ol3e, nl3e, _PAGE_PRESENT))
             return UPDATE_ENTRY(l3, pl3e, ol3e, nl3e, pfn, curr, preserve_ad);
 
         if ( unlikely(!get_page_from_l3e(nl3e, pfn, d)) )
             return 0;
+
+        adjust_guest_l3e(nl3e, d);
 
         if ( unlikely(!UPDATE_ENTRY(l3, pl3e, ol3e, nl3e, pfn, curr,
                                     preserve_ad)) )

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