x86: rmb() can be weakened according to new Intel spec.

Both Intel and AMD agree that, from a programmer's viewpoint:
 Loads cannot be reordered relative to other loads.
 Stores cannot be reordered relative to other stores.

Intel64 Architecture Memory Ordering White Paper
<http://developer.intel.com/products/processor/manuals/318147.pdf>

AMD64 Architecture Programmer's Manual, Volume 2: System Programming
<http://www.amd.com/us-en/assets/content_type/\
 white_papers_and_tech_docs/24593.pdf>

Signed-off-by: Keir Fraser <keir.fraser@eu.citrix.com>

diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
index 1217002643f0ff3e4eb5a31b85aeb026c5f8bbc0..c257513dadca89bdd09e17907d32ff329451936d 100644 (file)
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -135,6 +135,21 @@ static always_inline unsigned long __cmpxchg(
 
 #define __HAVE_ARCH_CMPXCHG
 
+/*
+ * Both Intel and AMD agree that, from a programmer's viewpoint:
+ *  Loads cannot be reordered relative to other loads.
+ *  Stores cannot be reordered relative to other stores.
+ * 
+ * Intel64 Architecture Memory Ordering White Paper
+ * <http://developer.intel.com/products/processor/manuals/318147.pdf>
+ * 
+ * AMD64 Architecture Programmer's Manual, Volume 2: System Programming
+ * <http://www.amd.com/us-en/assets/content_type/\
+ *  white_papers_and_tech_docs/24593.pdf>
+ */
+#define rmb()           barrier()
+#define wmb()           barrier()
+
 #ifdef CONFIG_SMP
 #define smp_mb()        mb()
 #define smp_rmb()       rmb()

diff --git a/xen/include/asm-x86/x86_32/system.h b/xen/include/asm-x86/x86_32/system.h
index cf28258d399bf6376cd516b0a6d19f9b3897437f..5707af8e8643f6b4ec40598b2358641eeeede84b 100644 (file)
--- a/xen/include/asm-x86/x86_32/system.h
+++ b/xen/include/asm-x86/x86_32/system.h
@@ -98,9 +98,8 @@ static inline void atomic_write64(uint64_t *p, uint64_t v)
         w = x;
 }
 
-#define mb()    asm volatile ( "lock; addl $0,0(%%esp)" : : : "memory" )
-#define rmb()   asm volatile ( "lock; addl $0,0(%%esp)" : : : "memory" )
-#define wmb()   asm volatile ( "" : : : "memory" )
+#define mb()                    \
+    asm volatile ( "lock; addl $0,0(%%esp)" : : : "memory" )
 
 #define __save_flags(x)         \
     asm volatile ( "pushfl ; popl %0" : "=g" (x) : )

diff --git a/xen/include/asm-x86/x86_64/system.h b/xen/include/asm-x86/x86_64/system.h
index 30902a01bc1af9d1f0ac3fce16a3f410327cb5fa..229fc15292ab175b954f3e3475033b44f9f87183 100644 (file)
--- a/xen/include/asm-x86/x86_64/system.h
+++ b/xen/include/asm-x86/x86_64/system.h
@@ -52,9 +52,8 @@ static inline void atomic_write64(uint64_t *p, uint64_t v)
     *p = v;
 }
 
-#define mb()    asm volatile ( "mfence" : : : "memory" )
-#define rmb()   asm volatile ( "lfence" : : : "memory" )
-#define wmb()   asm volatile ( "" : : : "memory" )
+#define mb()                    \
+    asm volatile ( "mfence" : : : "memory" )
 
 #define __save_flags(x)         \
     asm volatile ( "pushfq ; popq %q0" : "=g" (x) : :"memory" )