[PATCH] x86: implement always-locked bit ops, for memory shared with an SMP hypervisor

Add "always lock'd" implementations of set_bit, clear_bit and change_bit and
the corresponding test_and_ functions.  Also add "always lock'd"
implementation of cmpxchg.  These give guaranteed strong synchronisation and
are required for non-SMP kernels running on an SMP hypervisor.

Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index 098bcee94e38..a6dabbcd6e6a 100644
--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -267,6 +267,9 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz
 #define cmpxchg(ptr,o,n)\
         ((__typeof__(*(ptr)))__cmpxchg((ptr),(unsigned long)(o),\
                                         (unsigned long)(n),sizeof(*(ptr))))
+#define sync_cmpxchg(ptr,o,n)\
+        ((__typeof__(*(ptr)))__sync_cmpxchg((ptr),(unsigned long)(o),\
+                                        (unsigned long)(n),sizeof(*(ptr))))
 #endif
 
 static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
@@ -296,6 +299,39 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
         return old;
 }
 
+/*
+ * Always use locked operations when touching memory shared with a
+ * hypervisor, since the system may be SMP even if the guest kernel
+ * isn't.
+ */
+static inline unsigned long __sync_cmpxchg(volatile void *ptr,
+                                            unsigned long old,
+                                            unsigned long new, int size)
+{
+        unsigned long prev;
+        switch (size) {
+        case 1:
+                __asm__ __volatile__("lock; cmpxchgb %b1,%2"
+                                     : "=a"(prev)
+                                     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+                                     : "memory");
+                return prev;
+        case 2:
+                __asm__ __volatile__("lock; cmpxchgw %w1,%2"
+                                     : "=a"(prev)
+                                     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+                                     : "memory");
+                return prev;
+        case 4:
+                __asm__ __volatile__("lock; cmpxchgl %1,%2"
+                                     : "=a"(prev)
+                                     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+                                     : "memory");
+                return prev;
+        }
+        return old;
+}
+
 #ifndef CONFIG_X86_CMPXCHG
 /*
  * Building a kernel capable running on 80386. It may be necessary to