KVM: arm64: vgic-debug: Exit the iterator properly w/o LPI

In case the guest doesn't have any LPI, we previously relied on the
iterator setting

	'intid = nr_spis + VGIC_NR_PRIVATE_IRQS' && 'lpi_idx = 1'

to exit the iterator. But it was broken with commit 85d3ccc8 ("KVM:
arm64: vgic-debug: Use an xarray mark for debug iterator") -- the intid
remains at 'nr_spis + VGIC_NR_PRIVATE_IRQS - 1', and we end up endlessly
printing the last SPI's state.

Consider that it's meaningless to search the LPI xarray and populate
lpi_idx when there is no LPI, let's just skip the process for that case.

The result is that

* If there's no LPI, we focus on the intid and exit the iterator when it
  runs out of the valid SPI range.
* Otherwise we keep the current logic and let the xarray drive the
  iterator.

Fixes: 85d3ccc8 ("KVM: arm64: vgic-debug: Use an xarray mark for debug iterator")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240807052024.2084-1-yuzenghui@huawei.comSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/vgic/vgic-debug.c

@@ -45,7 +45,8 @@ static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
 	 * Let the xarray drive the iterator after the last SPI, as the iterator
 	 * has exhausted the sequentially-allocated INTID space.
 	 */
-	if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS - 1)) {
+	if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS - 1) &&
+	    iter->nr_lpis) {
 		if (iter->lpi_idx < iter->nr_lpis)
 			xa_find_after(&dist->lpi_xa, &iter->intid,
 				      VGIC_LPI_MAX_INTID,
@@ -112,7 +113,7 @@ static bool end_of_vgic(struct vgic_state_iter *iter)
 	return iter->dist_id > 0 &&
 		iter->vcpu_id == iter->nr_cpus &&
 		iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS) &&
-		iter->lpi_idx > iter->nr_lpis;
+		(!iter->nr_lpis || iter->lpi_idx > iter->nr_lpis);
 }
 
 static void *vgic_debug_start(struct seq_file *s, loff_t *pos)