x86: KVM guest: Add memory clobber to hypercalls

Hypercalls can modify arbitrary regions of memory.  Make sure to indicate this
in the clobber list.  This fixes a hang when using KVM_GUEST kernel built with
GCC 4.3.0.

This was originally spotted and analyzed by Marcelo.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NAvi Kivity <avi@qumranet.com>

include/asm-x86/kvm_para.h

@@ -71,7 +71,8 @@ static inline long kvm_hypercall0(unsigned int nr)
 	long ret;
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
-		     : "a"(nr));
+		     : "a"(nr)
+		     : "memory");
 	return ret;
 }
 
@@ -80,7 +81,8 @@ static inline long kvm_hypercall1(unsigned int nr, unsigned long p1)
 	long ret;
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
-		     : "a"(nr), "b"(p1));
+		     : "a"(nr), "b"(p1)
+		     : "memory");
 	return ret;
 }
 
@@ -90,7 +92,8 @@ static inline long kvm_hypercall2(unsigned int nr, unsigned long p1,
 	long ret;
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
-		     : "a"(nr), "b"(p1), "c"(p2));
+		     : "a"(nr), "b"(p1), "c"(p2)
+		     : "memory");
 	return ret;
 }
 
@@ -100,7 +103,8 @@ static inline long kvm_hypercall3(unsigned int nr, unsigned long p1,
 	long ret;
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
-		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3));
+		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3)
+		     : "memory");
 	return ret;
 }
 
@@ -111,7 +115,8 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
 	long ret;
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
-		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3), "S"(p4));
+		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3), "S"(p4)
+		     : "memory");
 	return ret;
 }