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>

arch/x86/include/asm/kvm_host.h

@@ -830,11 +830,12 @@ enum {
 asmlinkage void kvm_spurious_fault(void);
 extern bool kvm_rebooting;
 
-#define __kvm_handle_fault_on_reboot(insn) \
+#define ____kvm_handle_fault_on_reboot(insn, cleanup_insn)	\
 	"666: " insn "\n\t" \
 	"668: \n\t"                           \
 	".pushsection .fixup, \"ax\" \n" \
 	"667: \n\t" \
+	cleanup_insn "\n\t"		      \
 	"cmpb $0, kvm_rebooting \n\t"	      \
 	"jne 668b \n\t"      		      \
 	__ASM_SIZE(push) " $666b \n\t"	      \
@@ -844,6 +845,9 @@ extern bool kvm_rebooting;
 	_ASM_PTR " 666b, 667b \n\t" \
 	".popsection"
 
+#define __kvm_handle_fault_on_reboot(insn)		\
+	____kvm_handle_fault_on_reboot(insn, "")
+
 #define KVM_ARCH_WANT_MMU_NOTIFIER
 int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
 int kvm_age_hva(struct kvm *kvm, unsigned long hva);

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;
 }