KVM: PPC: Book3S PR: Take SRCU read lock around RTAS kvm_read_guest() call

This does for PR KVM what c9438092 ("KVM: PPC: Book3S HV: Take SRCU
read lock around kvm_read_guest() call") did for HV KVM, that is,
eliminate a "suspicious rcu_dereference_check() usage!" warning by
taking the SRCU lock around the call to kvmppc_rtas_hcall().

It also fixes a return of RESUME_HOST to return EMULATE_FAIL instead,
since kvmppc_h_pr() is supposed to return EMULATE_* values.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_pr_papr.c

@@ -267,6 +267,8 @@ static int kvmppc_h_pr_xics_hcall(struct kvm_vcpu *vcpu, u32 cmd)
 
 int kvmppc_h_pr(struct kvm_vcpu *vcpu, unsigned long cmd)
 {
+	int rc, idx;
+
 	if (cmd <= MAX_HCALL_OPCODE &&
 	    !test_bit(cmd/4, vcpu->kvm->arch.enabled_hcalls))
 		return EMULATE_FAIL;
@@ -299,8 +301,11 @@ int kvmppc_h_pr(struct kvm_vcpu *vcpu, unsigned long cmd)
 		break;
 	case H_RTAS:
 		if (list_empty(&vcpu->kvm->arch.rtas_tokens))
-			return RESUME_HOST;
-		if (kvmppc_rtas_hcall(vcpu))
+			break;
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
+		rc = kvmppc_rtas_hcall(vcpu);
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
+		if (rc)
 			break;
 		kvmppc_set_gpr(vcpu, 3, 0);
 		return EMULATE_DONE;