KVM: PPC: Book3S HV: XIVE: Fix potential page leak on error path

We need to check the host page size is big enough to accomodate the
EQ. Let's do this before taking a reference on the EQ page to avoid
a potential leak if the check fails.

Cc: stable@vger.kernel.org # v5.2
Fixes: 13ce3297 ("KVM: PPC: Book3S HV: XIVE: Add controls for the EQ configuration")
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_xive_native.c

@@ -630,12 +630,6 @@ static int kvmppc_xive_native_set_queue_config(struct kvmppc_xive *xive,
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 	gfn = gpa_to_gfn(kvm_eq.qaddr);
-	page = gfn_to_page(kvm, gfn);
-	if (is_error_page(page)) {
-		srcu_read_unlock(&kvm->srcu, srcu_idx);
-		pr_err("Couldn't get queue page %llx!\n", kvm_eq.qaddr);
-		return -EINVAL;
-	}
 
 	page_size = kvm_host_page_size(kvm, gfn);
 	if (1ull << kvm_eq.qshift > page_size) {
@@ -644,6 +638,13 @@ static int kvmppc_xive_native_set_queue_config(struct kvmppc_xive *xive,
 		return -EINVAL;
 	}
 
+	page = gfn_to_page(kvm, gfn);
+	if (is_error_page(page)) {
+		srcu_read_unlock(&kvm->srcu, srcu_idx);
+		pr_err("Couldn't get queue page %llx!\n", kvm_eq.qaddr);
+		return -EINVAL;
+	}
+
 	qaddr = page_to_virt(page) + (kvm_eq.qaddr & ~PAGE_MASK);
 	srcu_read_unlock(&kvm->srcu, srcu_idx);