[RFC v4 12/16] irqdomain: irq_domain_check_msi_remap

[Eric Auger <eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

This new function checks whether all platform and PCI
MSI 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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 include/linux/irqdomain.h |  5 +++++
 kernel/irq/irqdomain.c    | 24 ++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
index ab017b2..b279dd1 100644
--- a/include/linux/irqdomain.h
+++ b/include/linux/irqdomain.h
@@ -219,6 +219,7 @@ 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,
@@ -491,6 +492,10 @@ static inline struct irq_domain *irq_find_matching_fwnode(
 {
 	return NULL;
 }
+static inline bool irq_domain_check_msi_remap(void)
+{
+	return false;
+}
 #endif /* !CONFIG_IRQ_DOMAIN */
 
 #endif /* _LINUX_IRQDOMAIN_H */
diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 8c0a0ae..d9a6fc5 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -278,6 +278,30 @@ struct irq_domain *irq_find_matching_fwspec(struct irq_fwspec *fwspec,
 EXPORT_SYMBOL_GPL(irq_find_matching_fwspec);
 
 /**
+ * irq_domain_check_msi_remap() - Checks whether all PCI and
+ * platform MSI irq domains implement IRQ remapping
+ */
+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 (((h->bus_token & DOMAIN_BUS_PCI_MSI) ||
+		     (h->bus_token & DOMAIN_BUS_PLATFORM_MSI)) &&
+		    !(h->flags & IRQ_DOMAIN_FLAG_MSI_REMAP)) {
+			ret = false;
+			goto out;
+		}
+	}
+out:
+	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