[Xen-devel] [PATCH 14 of 36] x86_64: add sync_cmpxchg

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Add sync_cmpxchg to match 32-bit's sync_cmpxchg.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 include/asm-x86/cmpxchg_64.h |   37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/include/asm-x86/cmpxchg_64.h b/include/asm-x86/cmpxchg_64.h
--- a/include/asm-x86/cmpxchg_64.h
+++ b/include/asm-x86/cmpxchg_64.h
@@ -93,6 +93,39 @@
        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 @@
        ((__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);                              \



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