1 files changed, 37 insertions, 0 deletions

diff --git a/include/asm-x86/cmpxchg_64.h b/include/asm-x86/cmpxchg_64.h
index d9b26b9a28cf..17463ccf8166 100644
--- a/include/asm-x86/cmpxchg_64.h
+++ b/include/asm-x86/cmpxchg_64.h
@@ -93,6 +93,39 @@ 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;
+}
+
 static inline unsigned long __cmpxchg_local(volatile void *ptr,
                                             unsigned long old,
                                             unsigned long new, int size)
@@ -139,6 +172,10 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
         ((__typeof__(*(ptr)))__cmpxchg_local((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))))
 #define cmpxchg64_local(ptr, o, n)                                      \
 ({                                                                      \
         BUILD_BUG_ON(sizeof(*(ptr)) != 8);                              \