IOMMU/PCI: don't let domain cleanup continue when device de-assignment failed

Failure here could in principle mean the device may still be issuing DMA
requests, which would continue to be translated by the page tables the
device entry currently points at. With this we cannot allow the
subsequent cleanup step of freeing the page tables to occur, to prevent
use-after-free issues. We would need to accept, for the time being, that
in such a case the remaining domain resources will all be leaked, and
the domain will continue to exist as a zombie.

However, with flushes no longer timing out (and with proper timeout
detection for device I/O TLB flushing yet to be implemented), there's no
way anymore for failures to occur, except due to bugs elsewhere. Hence
the change here is merely a "just in case" one.

In order to continue the loop in spite of an error, we can't use
pci_get_pdev_by_domain() anymore. I have no idea why it was used here in
the first place, instead of the cheaper list iteration.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
master commit: f591755823
master date: 2021-06-25 14:06:55 +0200

xen/drivers/passthrough/pci.c

@@ -968,7 +968,7 @@ static int deassign_device(struct domain *d, uint16_t seg, uint8_t bus,
 
 int pci_release_devices(struct domain *d)
 {
-    struct pci_dev *pdev;
+    struct pci_dev *pdev, *tmp;
     u8 bus, devfn;
     int ret;
 
@@ -979,18 +979,15 @@ int pci_release_devices(struct domain *d)
         pcidevs_unlock();
         return ret;
     }
-    while ( (pdev = pci_get_pdev_by_domain(d, -1, -1, -1)) )
+    list_for_each_entry_safe ( pdev, tmp, &d->pdev_list, domain_list )
     {
         bus = pdev->bus;
         devfn = pdev->devfn;
-        if ( deassign_device(d, pdev->seg, bus, devfn) )
-            printk("domain %d: deassign device (%04x:%02x:%02x.%u) failed!\n",
-                   d->domain_id, pdev->seg, bus,
-                   PCI_SLOT(devfn), PCI_FUNC(devfn));
+        ret = deassign_device(d, pdev->seg, bus, devfn) ?: ret;
     }
     pcidevs_unlock();
 
-    return 0;
+    return ret;
 }
 
 #define PCI_CLASS_BRIDGE_HOST    0x0600