iommu/vt-d: Cure VF irqdomain hickup

The recent changes to store the MSI irqdomain pointer in struct device
missed that Intel DMAR does not register virtual function devices.  Due to
that a VF device gets the plain PCI-MSI domain assigned and then issues
compat MSI messages which get caught by the interrupt remapping unit.

Cure that by inheriting the irq domain from the physical function
device.

Ideally the irqdomain would be associated to the bus, but DMAR can have
multiple units and therefore irqdomains on a single bus. The VF 'bus' could
of course inherit the domain from the PF, but that'd be yet another x86
oddity.

Fixes: 85a8dfc ("iommm/vt-d: Store irq domain in struct device")
Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Link: https://lore.kernel.org/r/draft-87eekymlpz.fsf@nanos.tec.linutronix.de

drivers/iommu/intel/dmar.c

@@ -333,6 +333,11 @@ static void  dmar_pci_bus_del_dev(struct dmar_pci_notify_info *info)
 	dmar_iommu_notify_scope_dev(info);
 }
 
+static inline void vf_inherit_msi_domain(struct pci_dev *pdev)
+{
+	dev_set_msi_domain(&pdev->dev, dev_get_msi_domain(&pdev->physfn->dev));
+}
+
 static int dmar_pci_bus_notifier(struct notifier_block *nb,
 				 unsigned long action, void *data)
 {
@@ -342,8 +347,20 @@ static int dmar_pci_bus_notifier(struct notifier_block *nb,
 	/* Only care about add/remove events for physical functions.
 	 * For VFs we actually do the lookup based on the corresponding
 	 * PF in device_to_iommu() anyway. */
-	if (pdev->is_virtfn)
+	if (pdev->is_virtfn) {
+		/*
+		 * Ensure that the VF device inherits the irq domain of the
+		 * PF device. Ideally the device would inherit the domain
+		 * from the bus, but DMAR can have multiple units per bus
+		 * which makes this impossible. The VF 'bus' could inherit
+		 * from the PF device, but that's yet another x86'sism to
+		 * inflict on everybody else.
+		 */
+		if (action == BUS_NOTIFY_ADD_DEVICE)
+			vf_inherit_msi_domain(pdev);
 		return NOTIFY_DONE;
+	}
+
 	if (action != BUS_NOTIFY_ADD_DEVICE &&
 	    action != BUS_NOTIFY_REMOVED_DEVICE)
 		return NOTIFY_DONE;