[Xen-changelog] [xen-3.0-testing] [XEN] PTE updates do not need to use CMPXCHG instruction.

[Xen patchbot-3.0-testing <patchbot-3.0-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 532979a7807111ff387df950e314ed97dd411e6f
# Parent  fd961e9acb3fc4941614c5863e831ec43867ae95
[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-unstable changeset:   10362:9d46e53c75f7598ab25b76b7a491801d1b320f5f
xen-unstable date:        Fri Jun 16 15:22:03 2006 +0100

[XEN] Fix 10362 change to create_grant_va_mapping().
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
xen-unstable changeset:   10363:61a81fab2a029f029420a7dc0c2f73b783b45729
xen-unstable date:        Fri Jun 16 15:34:21 2006 +0100
---
 xen/arch/x86/mm.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff -r fd961e9acb3f -r 532979a78071 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Fri Jun 16 10:54:01 2006 +0100
+++ b/xen/arch/x86/mm.c Sat Jun 17 12:31:40 2006 +0100
@@ -1045,6 +1045,9 @@ 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);
 
@@ -1059,6 +1062,7 @@ static inline int update_l1e(l1_pgentry_
         return 0;
     }
     return 1;
+#endif
 }
 
 
@@ -1106,6 +1110,9 @@ 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),                      \
@@ -1117,6 +1124,7 @@ 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, 
@@ -2284,8 +2292,8 @@ 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) )
     {
         put_page_type(page);
         rc = GNTST_general_error;

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