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

arch/x86/kvm/vmx/vmenter.S

@@ -54,9 +54,9 @@ ENTRY(vmx_vmenter)
  ret
 
 3: cmpb $0, kvm_rebooting
- jne 4f
- call kvm_spurious_fault
-4: ret
+ je 4f
+ ret
+4: ud2
 
  .pushsection .fixup, "ax"
 5: jmp 3b