VT-d: fix (de)assign ordering when RMRRs are in use

In the event that the RMRR mappings are essential for device operation,
they should be established before updating the device's context entry,
while they should be torn down only after the device's context entry was
successfully updated.

Also adjust a related log message.

This is CVE-2022-26358 / part of XSA-400.

Fixes: 8b99f4400b ("VT-d: fix RMRR related error handling")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>

xen/drivers/passthrough/vtd/iommu.c

@@ -2409,6 +2409,10 @@ static int cf_check reassign_device_ownership(
 {
     int ret;
 
+    ret = domain_context_unmap(source, devfn, pdev);
+    if ( ret )
+        return ret;
+
     /*
      * If the device belongs to the hardware domain, and it has RMRR, don't
      * remove it from the hardware domain, because BIOS may use RMRR at
@@ -2437,10 +2441,6 @@ static int cf_check reassign_device_ownership(
             }
     }
 
-    ret = domain_context_unmap(source, devfn, pdev);
-    if ( ret )
-        return ret;
-
     if ( devfn == pdev->devfn && pdev->domain != dom_io )
     {
         list_move(&pdev->domain_list, &dom_io->pdev_list);
@@ -2525,9 +2525,8 @@ static int cf_check intel_iommu_assign_device(
         }
     }
 
-    ret = reassign_device_ownership(s, d, devfn, pdev);
-    if ( ret || d == dom_io )
-        return ret;
+    if ( d == dom_io )
+        return reassign_device_ownership(s, d, devfn, pdev);
 
     /* Setup rmrr identity mapping */
     for_each_rmrr_device( rmrr, bdf, i )
@@ -2540,20 +2539,37 @@ static int cf_check intel_iommu_assign_device(
                                          rmrr->end_address, flag);
             if ( ret )
             {
-                int rc;
-
-                rc = reassign_device_ownership(d, s, devfn, pdev);
                 printk(XENLOG_G_ERR VTDPREFIX
-                       " cannot map reserved region (%"PRIx64",%"PRIx64"] for Dom%d (%d)\n",
-                       rmrr->base_address, rmrr->end_address,
-                       d->domain_id, ret);
-                if ( rc )
-                {
-                    printk(XENLOG_ERR VTDPREFIX
-                           " failed to reclaim %pp from %pd (%d)\n",
-                           &PCI_SBDF3(seg, bus, devfn), d, rc);
-                    domain_crash(d);
-                }
+                       "%pd: cannot map reserved region [%"PRIx64",%"PRIx64"]: %d\n",
+                       d, rmrr->base_address, rmrr->end_address, ret);
+                break;
+            }
+        }
+    }
+
+    if ( !ret )
+        ret = reassign_device_ownership(s, d, devfn, pdev);
+
+    /* See reassign_device_ownership() for the hwdom aspect. */
+    if ( !ret || is_hardware_domain(d) )
+        return ret;
+
+    for_each_rmrr_device( rmrr, bdf, i )
+    {
+        if ( rmrr->segment == seg &&
+             PCI_BUS(bdf) == bus &&
+             PCI_DEVFN2(bdf) == devfn )
+        {
+            int rc = iommu_identity_mapping(d, p2m_access_x,
+                                            rmrr->base_address,
+                                            rmrr->end_address, 0);
+
+            if ( rc && rc != -ENOENT )
+            {
+                printk(XENLOG_ERR VTDPREFIX
+                       "%pd: cannot unmap reserved region [%"PRIx64",%"PRIx64"]: %d\n",
+                       d, rmrr->base_address, rmrr->end_address, rc);
+                domain_crash(d);
                 break;
             }
         }