irqdomain: irq_domain_check_msi_remap

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@redhat.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Tomasz Nowicki <tomasz.nowicki@caviumnetworks.com>
Tested-by: Tomasz Nowicki <tomasz.nowicki@caviumnetworks.com>
Tested-by: Bharat Bhushan <bharat.bhushan@nxp.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 876e13172dc8..80c4f9312187 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
  *