KVM: VMX: Move VMREAD cleanup to exception handler

We clean up a failed VMREAD by clearing the output register.  Do
it in the exception handler instead of unconditionally.  This is
worthwhile since there are more than a hundred call sites.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d48ec60ea421..7d22d6c6734d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -43,6 +43,8 @@
 #include "trace.h"
 
 #define __ex(x) __kvm_handle_fault_on_reboot(x)
+#define __ex_clear(x, reg) \
+        ____kvm_handle_fault_on_reboot(x, "xor " reg " , " reg)
 
 MODULE_AUTHOR("Qumranet");
 MODULE_LICENSE("GPL");
@@ -587,10 +589,10 @@ static inline void ept_sync_individual_addr(u64 eptp, gpa_t gpa)
 
 static unsigned long vmcs_readl(unsigned long field)
 {
-        unsigned long value = 0;
+        unsigned long value;
 
-        asm volatile (__ex(ASM_VMX_VMREAD_RDX_RAX)
-                      : "+a"(value) : "d"(field) : "cc");
+        asm volatile (__ex_clear(ASM_VMX_VMREAD_RDX_RAX, "%0")
+                      : "=a"(value) : "d"(field) : "cc");
         return value;
 }