x86/pci/xen: Fixup fallout from the PCI/MSI overhaul

David reported that the recent PCI/MSI rework results in MSI descriptor
leakage under XEN.

This is caused by:

  1) The missing MSI_FLAG_FREE_MSI_DESCS flag in the XEN MSI domain info,
     which is required now that PCI/MSI delegates descriptor freeing to
     the core MSI code.

  2) Not disassociating the interrupts on teardown, by setting the
     msi_desc::irq to 0. This was not required before because the teardown
     was unconditional and did not check whether a MSI descriptor was still
     connected to a Linux interrupt.

On further inspection it came to light that the MSI_FLAG_DEV_SYSFS is
missing in the XEN MSI domain info as well to restore the pre 6.2 status
quo.

Add the missing MSI flags and disassociate the MSI descriptor from the
Linux interrupt in the XEN specific teardown function.

Fixes: b2bdda20 ("PCI/MSI: Let the MSI core free descriptors")
Fixes: 2f2940d1 ("genirq/msi: Remove filter from msi_free_descs_free_range()")
Fixes: ffd84485 ("PCI/MSI: Let the irq code handle sysfs groups")
Reported-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/871qnunycr.ffs@tglx

arch/x86/pci/xen.c

@@ -392,6 +392,7 @@ static void xen_teardown_msi_irqs(struct pci_dev *dev)
 	msi_for_each_desc(msidesc, &dev->dev, MSI_DESC_ASSOCIATED) {
 		for (i = 0; i < msidesc->nvec_used; i++)
 			xen_destroy_irq(msidesc->irq + i);
+		msidesc->irq = 0;
 	}
 }
 
@@ -433,7 +434,7 @@ static struct msi_domain_ops xen_pci_msi_domain_ops = {
 };
 
 static struct msi_domain_info xen_pci_msi_domain_info = {
-	.flags			= MSI_FLAG_PCI_MSIX,
+	.flags			= MSI_FLAG_PCI_MSIX | MSI_FLAG_FREE_MSI_DESCS | MSI_FLAG_DEV_SYSFS,
 	.ops			= &xen_pci_msi_domain_ops,
 };