x86: asm/virtext.h: add cpu_vmxoff() inline function

Unfortunately we can't use exactly the same code from vmx
hardware_disable(), because the KVM function uses the
__kvm_handle_fault_on_reboot() tricks.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>

arch/x86/include/asm/virtext.h

@@ -18,6 +18,8 @@
 #include <asm/processor.h>
 #include <asm/system.h>
 
+#include <asm/vmx.h>
+
 /*
  * VMX functions:
  */
@@ -28,4 +30,17 @@ static inline int cpu_has_vmx(void)
 	return test_bit(5, &ecx); /* CPUID.1:ECX.VMX[bit 5] -> VT */
 }
 
+
+/** Disable VMX on the current CPU
+ *
+ * vmxoff causes a undefined-opcode exception if vmxon was not run
+ * on the CPU previously. Only call this function if you know VMX
+ * is enabled.
+ */
+static inline void cpu_vmxoff(void)
+{
+	asm volatile (ASM_VMX_VMXOFF : : : "cc");
+	write_cr4(read_cr4() & ~X86_CR4_VMXE);
+}
+
 #endif /* _ASM_X86_VIRTEX_H */