KVM: fix kvm_fix_hypercall() to return X86EMUL_*

This patch fixes kvm_fix_hypercall() to propagate X86EMUL_*
info generated by emulator_write_emulated() to its callers:
suggested by Marcelo.

The effect of this is x86_emulate_insn() will begin to handle
the page faults which occur in emulator_write_emulated():
this should be OK because emulator_write_emulated_onepage()
always injects page fault when emulator_write_emulated()
returns X86EMUL_PROPAGATE_FAULT.
Signed-off-by: NTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/x86.c

@@ -3888,10 +3888,8 @@ EXPORT_SYMBOL_GPL(kvm_emulate_hypercall);
 int kvm_fix_hypercall(struct kvm_vcpu *vcpu)
 {
 	char instruction[3];
-	int ret = 0;
 	unsigned long rip = kvm_rip_read(vcpu);
 
-
 	/*
 	 * Blow out the MMU to ensure that no other VCPU has an active mapping
 	 * to ensure that the updated hypercall appears atomically across all
@@ -3900,11 +3898,8 @@ int kvm_fix_hypercall(struct kvm_vcpu *vcpu)
 	kvm_mmu_zap_all(vcpu->kvm);
 
 	kvm_x86_ops->patch_hypercall(vcpu, instruction);
-	if (emulator_write_emulated(rip, instruction, 3, vcpu)
-	    != X86EMUL_CONTINUE)
-		ret = -EFAULT;
 
-	return ret;
+	return emulator_write_emulated(rip, instruction, 3, vcpu);
 }
 
 static u64 mk_cr_64(u64 curr_cr, u32 new_val)