irqchip/gic-v3-its: Don't map the MSI page in its_irq_compose_msi_msg()

its_irq_compose_msi_msg() may be called from non-preemptible context.
However, on RT, iommu_dma_map_msi_msg requires to be called from a
preemptible context.

A recent change split iommu_dma_map_msi_msg() in two new functions:
one that should be called in preemptible context, the other does
not have any requirement.

The GICv3 ITS driver is reworked to avoid executing preemptible code in
non-preemptible context. This can be achieved by preparing the MSI
mapping when allocating the MSI interrupt.
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-gic-v3-its.c

@@ -1178,7 +1178,7 @@ static void its_irq_compose_msi_msg(struct irq_data *d, struct msi_msg *msg)
 	msg->address_hi		= upper_32_bits(addr);
 	msg->data		= its_get_event_id(d);
 
-	iommu_dma_map_msi_msg(d->irq, msg);
+	iommu_dma_compose_msi_msg(irq_data_get_msi_desc(d), msg);
 }
 
 static int its_irq_set_irqchip_state(struct irq_data *d,
@@ -2563,6 +2563,7 @@ static int its_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
 {
 	msi_alloc_info_t *info = args;
 	struct its_device *its_dev = info->scratchpad[0].ptr;
+	struct its_node *its = its_dev->its;
 	irq_hw_number_t hwirq;
 	int err;
 	int i;
@@ -2571,6 +2572,10 @@ static int its_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
 	if (err)
 		return err;
 
+	err = iommu_dma_prepare_msi(info->desc, its->get_msi_base(its_dev));
+	if (err)
+		return err;
+
 	for (i = 0; i < nr_irqs; i++) {
 		err = its_irq_gic_domain_alloc(domain, virq + i, hwirq + i);
 		if (err)