x86/kvm: Replace vmx_vmenter()'s call to kvm_spurious_fault() with UD2

Objtool reports the following:

  arch/x86/kvm/vmx/vmenter.o: warning: objtool: vmx_vmenter()+0x14: call without frame pointer save/setup

But frame pointers are necessarily broken anyway, because
__vmx_vcpu_run() clobbers RBP with the guest's value before calling
vmx_vmenter().  So calling without a frame pointer doesn't make things
any worse.

Make objtool happy by changing the call to a UD2.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/9fc2216c9dc972f95bb65ce2966a682c6bda1cb0.1563413318.git.jpoimboe@redhat.com

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index d4cb194..4010d51 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -54,9 +54,9 @@
 3:	cmpb $0, kvm_rebooting
-	jne 4f
-	call kvm_spurious_fault
-4:	ret
+	je 4f
+	ret
+4:	ud2
 	.pushsection .fixup, "ax"
 5:	jmp 3b