KVM: PPC: set IN_GUEST_MODE before checking requests

Avoid a race as described in the code comment.

Also remove a related smp_wmb() from booke's kvmppc_prepare_to_enter().
I can't see any reason for it, and the book3s_pr version doesn't have it.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/booke.c

@@ -674,7 +674,6 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 
 out:
 	vcpu->mode = OUTSIDE_GUEST_MODE;
-	smp_wmb();
 	return ret;
 }
 

arch/powerpc/kvm/powerpc.c

@@ -78,7 +78,16 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			break;
 		}
 
+		vcpu->mode = IN_GUEST_MODE;
+
+		/*
+		 * Reading vcpu->requests must happen after setting vcpu->mode,
+		 * so we don't miss a request because the requester sees
+		 * OUTSIDE_GUEST_MODE and assumes we'll be checking requests
+		 * before next entering the guest (and thus doesn't IPI).
+		 */
 		smp_mb();
+
 		if (vcpu->requests) {
 			/* Make sure we process requests preemptable */
 			local_irq_enable();
@@ -111,11 +120,6 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 #endif
 
 		kvm_guest_enter();
-
-		/* Going into guest context! Yay! */
-		vcpu->mode = IN_GUEST_MODE;
-		smp_wmb();
-
 		break;
 	}