VT-d: undo device mappings upon error

When
 - flushes (supposedly not possible anymore after XSA-373),
 - secondary mappings for legacy PCI devices behind bridges,
 - secondary mappings for chipset quirks, or
 - find_upstream_bridge() invocations
fail, the successfully established device mappings should not be left
around.

Further, when (parts of) unmapping fail, simply returning an error is
typically not enough. Crash the domain instead in such cases, arranging
for domain cleanup to continue in a best effort manner despite such
failures.

Finally make domain_context_unmap()'s error behavior consistent in the
legacy PCI device case: Don't bail from the function in one special
case, but always just exit the switch statement.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
master commit: f3401d65d9
master date: 2021-06-24 16:28:25 +0200

xen/drivers/passthrough/vtd/iommu.c

@@ -1463,9 +1463,15 @@ int domain_context_mapping_one(
     if ( !seg && !rc )
         rc = me_wifi_quirk(domain, bus, devfn, MAP_ME_PHANTOM_FUNC);
 
+    if ( rc )
+        domain_context_unmap_one(domain, iommu, bus, devfn);
+
     return rc;
 }
 
+static int domain_context_unmap(struct domain *d, uint8_t devfn,
+                                struct pci_dev *pdev);
+
 static int domain_context_mapping(struct domain *domain, u8 devfn,
                                   struct pci_dev *pdev)
 {
@@ -1529,16 +1535,21 @@ static int domain_context_mapping(struct domain *domain, u8 devfn,
         if ( ret )
             break;
 
-        if ( find_upstream_bridge(seg, &bus, &devfn, &secbus) < 1 )
-            break;
+        if ( (ret = find_upstream_bridge(seg, &bus, &devfn, &secbus)) < 1 )
+        {
+            if ( !ret )
+                break;
+            ret = -ENXIO;
+        }
 
         /*
          * Mapping a bridge should, if anything, pass the struct pci_dev of
          * that bridge. Since bridges don't normally get assigned to guests,
          * their owner would be the wrong one. Pass NULL instead.
          */
-        ret = domain_context_mapping_one(domain, drhd->iommu, bus, devfn,
-                                         NULL);
+        if ( ret >= 0 )
+            ret = domain_context_mapping_one(domain, drhd->iommu, bus, devfn,
+                                             NULL);
 
         /*
          * Devices behind PCIe-to-PCI/PCIx bridge may generate different
@@ -1555,6 +1566,9 @@ static int domain_context_mapping(struct domain *domain, u8 devfn,
             ret = domain_context_mapping_one(domain, drhd->iommu, secbus, 0,
                                              NULL);
 
+        if ( ret )
+            domain_context_unmap(domain, devfn, pdev);
+
         break;
 
     default:
@@ -1634,6 +1648,19 @@ int domain_context_unmap_one(
     if ( !iommu->drhd->segment && !rc )
         rc = me_wifi_quirk(domain, bus, devfn, UNMAP_ME_PHANTOM_FUNC);
 
+    if ( rc && !is_hardware_domain(domain) && domain != dom_io )
+    {
+        if ( domain->is_dying )
+        {
+            printk(XENLOG_ERR "%pd: error %d unmapping %04x:%02x:%02x.%u\n",
+                   domain, rc, iommu->drhd->segment, bus,
+                   PCI_SLOT(devfn), PCI_FUNC(devfn));
+            rc = 0; /* Make upper layers continue in a best effort manner. */
+        }
+        else
+            domain_crash(domain);
+    }
+
     return rc;
 }
 
@@ -1688,17 +1715,29 @@ static int domain_context_unmap(struct domain *domain, u8 devfn,
 
         tmp_bus = bus;
         tmp_devfn = devfn;
-        if ( find_upstream_bridge(seg, &tmp_bus, &tmp_devfn, &secbus) < 1 )
+        if ( (ret = find_upstream_bridge(seg, &tmp_bus, &tmp_devfn,
+                                         &secbus)) < 1 )
+        {
+            if ( ret )
+            {
+                ret = -ENXIO;
+                if ( !domain->is_dying &&
+                     !is_hardware_domain(domain) && domain != dom_io )
+                {
+                    domain_crash(domain);
+                    /* Make upper layers continue in a best effort manner. */
+                    ret = 0;
+                }
+            }
             break;
+        }
 
         /* PCIe to PCI/PCIx bridge */
         if ( pdev_type(seg, tmp_bus, tmp_devfn) == DEV_TYPE_PCIe2PCI_BRIDGE )
         {
             ret = domain_context_unmap_one(domain, iommu, tmp_bus, tmp_devfn);
-            if ( ret )
-                return ret;
-
-            ret = domain_context_unmap_one(domain, iommu, secbus, 0);
+            if ( !ret )
+                ret = domain_context_unmap_one(domain, iommu, secbus, 0);
         }
         else /* Legacy PCI bridge */
             ret = domain_context_unmap_one(domain, iommu, tmp_bus, tmp_devfn);