x86: Add memory modify constraints to xchg() and cmpxchg()

commit 113fc5a6e8c2288619ff7e8187a6f556b7e0d372 upstream.

xchg() and cmpxchg() modify their memory operands, not merely read
them.  For some versions of gcc the "memory" clobber has apparently
dealt with the situation, but not for all.

Originally-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Glauber Costa <glommer@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Peter Palfrader <peter@palfrader.org>
Cc: Greg KH <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Zachary Amsden <zamsden@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
LKML-Reference: <4C4F7277.8050306@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 89 insertions, 85 deletions

diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index ee1931be6593..5af505158515 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -34,12 +34,12 @@ static inline void __set_64bit(unsigned long long *ptr,
 			       unsigned int low, unsigned int high)
 {
 	asm volatile("\n1:\t"
-		     "movl (%0), %%eax\n\t"
-		     "movl 4(%0), %%edx\n\t"
-		     LOCK_PREFIX "cmpxchg8b (%0)\n\t"
+		     "movl (%1), %%eax\n\t"
+		     "movl 4(%1), %%edx\n\t"
+		     LOCK_PREFIX "cmpxchg8b %0\n\t"
 		     "jnz 1b"
-		     : /* no outputs */
-		     : "D"(ptr),
+		     : "=m"(*ptr)
+		     : "D" (ptr),
 		       "b"(low),
 		       "c"(high)
 		     : "ax", "dx", "memory");
@@ -82,20 +82,20 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
 	switch (size) {
 	case 1:
 		asm volatile("xchgb %b0,%1"
-			     : "=q" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=q" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	case 2:
 		asm volatile("xchgw %w0,%1"
-			     : "=r" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=r" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	case 4:
 		asm volatile("xchgl %0,%1"
-			     : "=r" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=r" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	}
@@ -139,21 +139,21 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	unsigned long prev;
 	switch (size) {
 	case 1:
-		asm volatile(LOCK_PREFIX "cmpxchgb %b1,%2"
-			     : "=a"(prev)
-			     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgb %b2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "q"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 2:
-		asm volatile(LOCK_PREFIX "cmpxchgw %w1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgw %w2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 4:
-		asm volatile(LOCK_PREFIX "cmpxchgl %1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgl %2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	}
@@ -172,21 +172,21 @@ static inline unsigned long __sync_cmpxchg(volatile void *ptr,
 	unsigned long prev;
 	switch (size) {
 	case 1:
-		asm volatile("lock; cmpxchgb %b1,%2"
-			     : "=a"(prev)
-			     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("lock; cmpxchgb %b2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "q"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 2:
-		asm volatile("lock; cmpxchgw %w1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("lock; cmpxchgw %w2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 4:
-		asm volatile("lock; cmpxchgl %1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("lock; cmpxchgl %2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	}
@@ -200,21 +200,21 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
 	unsigned long prev;
 	switch (size) {
 	case 1:
-		asm volatile("cmpxchgb %b1,%2"
-			     : "=a"(prev)
-			     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgb %b2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "q"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 2:
-		asm volatile("cmpxchgw %w1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgw %w2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 4:
-		asm volatile("cmpxchgl %1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgl %2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	}
@@ -226,11 +226,10 @@ static inline unsigned long long __cmpxchg64(volatile void *ptr,
 					     unsigned long long new)
 {
 	unsigned long long prev;
-	asm volatile(LOCK_PREFIX "cmpxchg8b %3"
-		     : "=A"(prev)
+	asm volatile(LOCK_PREFIX "cmpxchg8b %1"
+		     : "=A"(prev), "+m" (*__xg(ptr))
 		     : "b"((unsigned long)new),
 		       "c"((unsigned long)(new >> 32)),
-		       "m"(*__xg(ptr)),
 		       "0"(old)
 		     : "memory");
 	return prev;
@@ -241,11 +240,10 @@ static inline unsigned long long __cmpxchg64_local(volatile void *ptr,
 						   unsigned long long new)
 {
 	unsigned long long prev;
-	asm volatile("cmpxchg8b %3"
-		     : "=A"(prev)
+	asm volatile("cmpxchg8b %1"
+		     : "=A"(prev), "+m"(*__xg(ptr))
 		     : "b"((unsigned long)new),
 		       "c"((unsigned long)(new >> 32)),
-		       "m"(*__xg(ptr)),
 		       "0"(old)
 		     : "memory");
 	return prev;
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 52de72e0de8c..1871cb045b01 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -26,26 +26,26 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
 	switch (size) {
 	case 1:
 		asm volatile("xchgb %b0,%1"
-			     : "=q" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=q" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	case 2:
 		asm volatile("xchgw %w0,%1"
-			     : "=r" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=r" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	case 4:
 		asm volatile("xchgl %k0,%1"
-			     : "=r" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=r" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	case 8:
 		asm volatile("xchgq %0,%1"
-			     : "=r" (x)
-			     : "m" (*__xg(ptr)), "0" (x)
+			     : "=r" (x), "+m" (*__xg(ptr))
+			     : "0" (x)
 			     : "memory");
 		break;
 	}
@@ -66,27 +66,27 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	unsigned long prev;
 	switch (size) {
 	case 1:
-		asm volatile(LOCK_PREFIX "cmpxchgb %b1,%2"
-			     : "=a"(prev)
-			     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgb %b2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "q"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 2:
-		asm volatile(LOCK_PREFIX "cmpxchgw %w1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgw %w2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 4:
-		asm volatile(LOCK_PREFIX "cmpxchgl %k1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgl %k2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 8:
-		asm volatile(LOCK_PREFIX "cmpxchgq %1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile(LOCK_PREFIX "cmpxchgq %2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	}
@@ -105,21 +105,27 @@ static inline unsigned long __sync_cmpxchg(volatile void *ptr,
 	unsigned long prev;
 	switch (size) {
 	case 1:
-		asm volatile("lock; cmpxchgb %b1,%2"
-			     : "=a"(prev)
-			     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("lock; cmpxchgb %b2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "q"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 2:
-		asm volatile("lock; cmpxchgw %w1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("lock; cmpxchgw %w2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 4:
-		asm volatile("lock; cmpxchgl %1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("lock; cmpxchgl %k2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
+			     : "memory");
+		return prev;
+	case 8:
+		asm volatile("lock; cmpxchgq %2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	}
@@ -133,27 +139,27 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
 	unsigned long prev;
 	switch (size) {
 	case 1:
-		asm volatile("cmpxchgb %b1,%2"
-			     : "=a"(prev)
-			     : "q"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgb %b2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "q"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 2:
-		asm volatile("cmpxchgw %w1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgw %w2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 4:
-		asm volatile("cmpxchgl %k1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgl %k2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	case 8:
-		asm volatile("cmpxchgq %1,%2"
-			     : "=a"(prev)
-			     : "r"(new), "m"(*__xg(ptr)), "0"(old)
+		asm volatile("cmpxchgq %2,%1"
+			     : "=a"(prev), "+m"(*__xg(ptr))
+			     : "r"(new), "0"(old)
 			     : "memory");
 		return prev;
 	}