linux-kernel - [PATCH 14 of 36] x86_64: add sync

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Date:	Wed, 25 Jun 2008 00:19:10 -0400
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	xen-devel <xen-devel@...ts.xensource.com>,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>, x86@...nel.org
Subject: [PATCH 14 of 36] x86_64: add sync_cmpxchg

Add sync_cmpxchg to match 32-bit's sync_cmpxchg.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 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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