[xen stable-4.15] IOMMU/PCI: don't let domain cleanup continue when device de-assignment failed

[patchbot@xxxxxxx]

commit 7b658fd273f9697975572585e1c80685b287dce9
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jul 15 09:22:18 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 15 09:22:18 2021 +0200

    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@xxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    master commit: f591755823a7e94fc6b4b8ddce71f0421a94fa09
    master date: 2021-06-25 14:06:55 +0200
---
 xen/drivers/passthrough/pci.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 705137f8be..a9e3ac906f 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -894,7 +894,7 @@ 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;
 
@@ -905,15 +905,15 @@ 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;
-        deassign_device(d, pdev->seg, bus, devfn);
+        ret = deassign_device(d, pdev->seg, bus, devfn) ?: ret;
     }
     pcidevs_unlock();
 
-    return 0;
+    return ret;
 }
 
 #define PCI_CLASS_BRIDGE_HOST    0x0600
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15