[PATCH] Add memory clobber to hypercalls (v2)

[Anthony Liguori]

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.

Since v1, I've also added a "m" constraint for the inputs to the hypercall.
This was suggested by Christian since it's not entirely clear whether a memory
clobber will force the data to be in memory before the asm statement.  In the
very least, it helps to be more conservative.

Signed-off-by: Anthony Liguori <[EMAIL PROTECTED]>

diff --git a/include/asm-x86/kvm_para.h b/include/asm-x86/kvm_para.h
index bfd9900..a621f10 100644
--- a/include/asm-x86/kvm_para.h
+++ b/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 +81,9 @@ 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),
+                      "m"(*(char *)p1)
+                    : "memory");
        return ret;
 }
 
@@ -90,7 +93,9 @@ 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),
+                      "m"(*(char *)p1), "m"(*(char *)p2)
+                    : "memory");
        return ret;
 }
 
@@ -100,7 +105,9 @@ 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),
+                      "m"(*(char *)p1), "m"(*(char *)p2), "m"(*(char *)p3)
+                    : "memory");
        return ret;
 }
 
@@ -111,7 +118,10 @@ 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),
+                      "m"(*(char *)p1), "m"(*(char *)p2), "m"(*(char *)p3),
+                      "m"(*(char *)p4)
+                    : "memory");
        return ret;
 }
 
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