KVM: arm64: vgic-v3: Iterate the xarray to find pending LPIs

Start walking the LPI xarray to find pending LPIs in preparation for
the removal of the LPI linked-list. Note that the 'basic' iterator
is chosen here as each iteration needs to drop the xarray read lock
(RCU) as reads/writes to guest memory can potentially block.
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240221054253.3848076-4-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/vgic/vgic-v3.c

@@ -380,6 +380,7 @@ int vgic_v3_save_pending_tables(struct kvm *kvm)
 	struct vgic_irq *irq;
 	gpa_t last_ptr = ~(gpa_t)0;
 	bool vlpi_avail = false;
+	unsigned long index;
 	int ret = 0;
 	u8 val;
 
@@ -396,7 +397,7 @@ int vgic_v3_save_pending_tables(struct kvm *kvm)
 		vlpi_avail = true;
 	}
 
-	list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
+	xa_for_each(&dist->lpi_xa, index, irq) {
 		int byte_offset, bit_nr;
 		struct kvm_vcpu *vcpu;
 		gpa_t pendbase, ptr;