# HG changeset patch
# User kfraser@xxxxxxxxxxxxxxxxxxxxxxx
# Node ID 9d46e53c75f7598ab25b76b7a491801d1b320f5f
# Parent 2ac74e1df3d7d7751a128d2ad2fe9cc3a9d23c54
[XEN] PTE updates do not need to use CMPXCHG instruction.
This is because the updates are already protected by a
per-domain lock. Using straightforward memory writes has
two advantages:
1. Faster
2. More correct (previously we could race accessed/dirty
bit updates by other CPUs).
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
xen/arch/x86/mm.c | 24 +++++++++++++++++++++---
1 files changed, 21 insertions(+), 3 deletions(-)
diff -r 2ac74e1df3d7 -r 9d46e53c75f7 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Fri Jun 16 14:45:01 2006 +0100
+++ b/xen/arch/x86/mm.c Fri Jun 16 15:22:03 2006 +0100
@@ -1167,6 +1167,9 @@ static inline int update_l1e(l1_pgentry_
l1_pgentry_t ol1e,
l1_pgentry_t nl1e)
{
+#ifndef PTE_UPDATE_WITH_CMPXCHG
+ return !__copy_to_user(pl1e, &nl1e, sizeof(nl1e));
+#else
intpte_t o = l1e_get_intpte(ol1e);
intpte_t n = l1e_get_intpte(nl1e);
@@ -1181,6 +1184,7 @@ static inline int update_l1e(l1_pgentry_
return 0;
}
return 1;
+#endif
}
@@ -1228,6 +1232,9 @@ static int mod_l1_entry(l1_pgentry_t *pl
return 1;
}
+#ifndef PTE_UPDATE_WITH_CMPXCHG
+#define UPDATE_ENTRY(_t,_p,_o,_n) ({ (*(_p) = (_n)); 1; })
+#else
#define UPDATE_ENTRY(_t,_p,_o,_n) ({ \
intpte_t __o = cmpxchg((intpte_t *)(_p), \
_t ## e_get_intpte(_o), \
@@ -1239,6 +1246,7 @@ static int mod_l1_entry(l1_pgentry_t *pl
(_t ## e_get_intpte(_n)), \
(__o)); \
(__o == _t ## e_get_intpte(_o)); })
+#endif
/* Update the L2 entry at pl2e to new value nl2e. pl2e is within frame pfn. */
static int mod_l2_entry(l2_pgentry_t *pl2e,
@@ -2408,12 +2416,16 @@ static int create_grant_pte_mapping(
goto failed;
}
- if ( __copy_from_user(&ol1e, (l1_pgentry_t *)va, sizeof(ol1e)) ||
- !update_l1e(va, ol1e, _nl1e) )
- {
+ ol1e = *(l1_pgentry_t *)va;
+ if ( !update_l1e(va, ol1e, _nl1e) )
+ {
+#ifndef PTE_UPDATE_WITH_CMPXCHG
+ BUG();
+#else
put_page_type(page);
rc = GNTST_general_error;
goto failed;
+#endif
}
put_page_from_l1e(ol1e, d);
@@ -2531,7 +2543,13 @@ static int create_grant_va_mapping(
if ( unlikely(__copy_from_user(&ol1e, pl1e, sizeof(ol1e)) != 0) ||
!update_l1e(pl1e, ol1e, _nl1e) )
+ {
+#ifndef PTE_UPDATE_WITH_CMPXCHG
+ BUG();
+#else
return GNTST_general_error;
+#endif
+ }
put_page_from_l1e(ol1e, d);
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