[PATCH v9 14/18] irqdomain: irq_domain_check_msi_remap

[Eric Auger]

This new function checks whether all MSI irq domains
implement IRQ remapping. This is useful to understand
whether VFIO passthrough is safe with respect to interrupts.

On ARM typically an MSI controller can sit downstream
to the IOMMU without preventing VFIO passthrough.
As such any assigned device can write into the MSI doorbell.
In case the MSI controller implements IRQ remapping, assigned
devices will not be able to trigger interrupts towards the
host. On the contrary, the assignment must be emphasized as
unsafe with respect to interrupts.

Signed-off-by: Eric Auger <eric.auger at redhat.com>
Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
Reviewed-by: Tomasz Nowicki <tomasz.nowicki at caviumnetworks.com>
Tested-by: Tomasz Nowicki <tomasz.nowicki at caviumnetworks.com>
Tested-by: Bharat Bhushan <bharat.bhushan at nxp.com>

---
v8 -> v9:
- reword doc comment

v7 -> v8:
- remove goto in irq_domain_check_msi_remap
- Added Marc's R-b

v5 -> v6:
- use irq_domain_hierarchical_is_msi_remap()
- comment rewording

v4 -> v5:
- Handle DOMAIN_BUS_FSL_MC_MSI domains
- Check parents
---
 include/linux/irqdomain.h |  1 +
 kernel/irq/irqdomain.c    | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
index bc2f571..188eced 100644
--- a/include/linux/irqdomain.h
+++ b/include/linux/irqdomain.h
@@ -222,6 +222,7 @@ struct irq_domain *irq_domain_add_legacy(struct device_node *of_node,
 					 void *host_data);
 extern struct irq_domain *irq_find_matching_fwspec(struct irq_fwspec *fwspec,
 						   enum irq_domain_bus_token bus_token);
+extern bool irq_domain_check_msi_remap(void);
 extern void irq_set_default_host(struct irq_domain *host);
 extern int irq_domain_alloc_descs(int virq, unsigned int nr_irqs,
 				  irq_hw_number_t hwirq, int node,
diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 876e131..80c4f93 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -278,6 +278,31 @@ struct irq_domain *irq_find_matching_fwspec(struct irq_fwspec *fwspec,
 EXPORT_SYMBOL_GPL(irq_find_matching_fwspec);
 
 /**
+ * irq_domain_check_msi_remap - Check whether all MSI irq domains implement
+ * IRQ remapping
+ *
+ * Return: false if any MSI irq domain does not support IRQ remapping,
+ * true otherwise (including if there is no MSI irq domain)
+ */
+bool irq_domain_check_msi_remap(void)
+{
+	struct irq_domain *h;
+	bool ret = true;
+
+	mutex_lock(&irq_domain_mutex);
+	list_for_each_entry(h, &irq_domain_list, link) {
+		if (irq_domain_is_msi(h) &&
+		    !irq_domain_hierarchical_is_msi_remap(h)) {
+			ret = false;
+			break;
+		}
+	}
+	mutex_unlock(&irq_domain_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(irq_domain_check_msi_remap);
+
+/**
  * irq_set_default_host() - Set a "default" irq domain
  * @domain: default domain pointer
  *
-- 
1.9.1