KVM: VMX: Use the kernel's version of VMXOFF

Drop kvm_cpu_vmxoff() in favor of the kernel's cpu_vmxoff().  Modify the
latter to return -EIO on fault so that KVM can invoke
kvm_spurious_fault() when appropriate.  In addition to the obvious code
reuse, dropping kvm_cpu_vmxoff() also eliminates VMX's last usage of the
__ex()/__kvm_handle_fault_on_reboot() macros, thus helping pave the way
toward dropping them entirely.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20201231002702.22237077-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/virtext.h

@@ -41,13 +41,18 @@ static inline int cpu_has_vmx(void)
  * faults are guaranteed to be due to the !post-VMXON check unless the CPU is
  * magically in RM, VM86, compat mode, or at CPL>0.
  */
-static inline void cpu_vmxoff(void)
+static inline int cpu_vmxoff(void)
 {
 	asm_volatile_goto("1: vmxoff\n\t"
 			  _ASM_EXTABLE(1b, %l[fault])
 			  ::: "cc", "memory" : fault);
+
+	cr4_clear_bits(X86_CR4_VMXE);
+	return 0;
+
 fault:
 	cr4_clear_bits(X86_CR4_VMXE);
+	return -EIO;
 }
 
 static inline int cpu_vmx_enabled(void)

arch/x86/kvm/vmx/vmx.c

@@ -2369,21 +2369,12 @@ static void vmclear_local_loaded_vmcss(void)
 		__loaded_vmcs_clear(v);
 }
 
-
-/* Just like cpu_vmxoff(), but with the __kvm_handle_fault_on_reboot()
- * tricks.
- */
-static void kvm_cpu_vmxoff(void)
-{
-	asm volatile (__ex("vmxoff"));
-
-	cr4_clear_bits(X86_CR4_VMXE);
-}
-
 static void hardware_disable(void)
 {
 	vmclear_local_loaded_vmcss();
-	kvm_cpu_vmxoff();
+
+	if (cpu_vmxoff())
+		kvm_spurious_fault();
 
 	intel_pt_handle_vmx(0);
 }