# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1237300166 0
# Node ID 6d5aa622fb3d696144ff7ea96636318946c560a8
# Parent 2725f82a7dca76b8ec6d979dbaba46303c915ed2
x86 shadow: Prevent in-sync L1s to become writable
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
xen/arch/x86/mm/shadow/multi.c | 22 +++++++++++++---------
1 files changed, 13 insertions(+), 9 deletions(-)
diff -r 2725f82a7dca -r 6d5aa622fb3d xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c Tue Mar 17 14:28:33 2009 +0000
+++ b/xen/arch/x86/mm/shadow/multi.c Tue Mar 17 14:29:26 2009 +0000
@@ -3123,6 +3123,19 @@ static int sh_page_fault(struct vcpu *v,
shadow_lock(d);
TRACE_CLEAR_PATH_FLAGS;
+
+ /* Make sure there is enough free shadow memory to build a chain of
+ * shadow tables. (We never allocate a top-level shadow on this path,
+ * only a 32b l1, pae l1, or 64b l3+2+1. Note that while
+ * SH_type_l1_shadow isn't correct in the latter case, all page
+ * tables are the same size there.)
+ *
+ * Preallocate shadow pages *before* removing writable accesses
+ * otherwhise an OOS L1 might be demoted and promoted again with
+ * writable mappings. */
+ shadow_prealloc(d,
+ SH_type_l1_shadow,
+ GUEST_PAGING_LEVELS < 4 ? 1 : GUEST_PAGING_LEVELS - 1);
rc = gw_remove_write_accesses(v, va, &gw);
@@ -3155,15 +3168,6 @@ static int sh_page_fault(struct vcpu *v,
shadow_audit_tables(v);
sh_audit_gw(v, &gw);
-
- /* Make sure there is enough free shadow memory to build a chain of
- * shadow tables. (We never allocate a top-level shadow on this path,
- * only a 32b l1, pae l1, or 64b l3+2+1. Note that while
- * SH_type_l1_shadow isn't correct in the latter case, all page
- * tables are the same size there.) */
- shadow_prealloc(d,
- SH_type_l1_shadow,
- GUEST_PAGING_LEVELS < 4 ? 1 : GUEST_PAGING_LEVELS - 1);
/* Acquire the shadow. This must happen before we figure out the rights
* for the shadow entry, since we might promote a page here. */
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