AMD/IOMMU: don't "add" IOMMUs

For find_iommu_for_device() to consistently (independent of ACPI tables)
return NULL for the PCI devices corresponding to IOMMUs, make sure
IOMMUs don't get mapped to themselves by ivrs_mappings[].

While amd_iommu_add_device() won't be called for IOMMUs from
pci_add_device(), as IOMMUs have got marked r/o,
_setup_hwdom_pci_devices() calls there nevertheless. Avoid issuing the
bogus debugging only "No iommu for ...; cannot be handed to ..." log
message as well as the non-debugging "setup ... for ... failed (-19)"
one.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Brian Woods <brian.woods@amd.com>

xen/drivers/passthrough/amd/iommu_acpi.c

@@ -81,8 +81,8 @@ static void __init add_ivrs_mapping_entry(
              ivrs_mappings[alias_id].intremap_inuse = shared_intremap_inuse;
          }
     }
-    /* assgin iommu hardware */
-    ivrs_mappings[bdf].iommu = iommu;
+    /* Assign IOMMU hardware, but don't map an IOMMU by itself. */
+    ivrs_mappings[bdf].iommu = iommu->bdf != bdf ? iommu : NULL;
 }
 
 static struct amd_iommu * __init find_iommu_from_bdf_cap(

xen/drivers/passthrough/amd/pci_amd_iommu.c

@@ -43,7 +43,7 @@ struct amd_iommu *find_iommu_for_device(int seg, int bdf)
     {
         unsigned int bd0 = bdf & ~PCI_FUNC(~0);
 
-        if ( ivrs_mappings[bd0].iommu )
+        if ( ivrs_mappings[bd0].iommu && ivrs_mappings[bd0].iommu->bdf != bdf )
         {
             struct ivrs_mappings tmp = ivrs_mappings[bd0];
 
@@ -424,6 +424,11 @@ static int amd_iommu_add_device(u8 devfn, struct pci_dev *pdev)
         return -EINVAL;
 
     bdf = PCI_BDF2(pdev->bus, pdev->devfn);
+
+    for_each_amd_iommu(iommu)
+        if ( pdev->seg == iommu->seg && bdf == iommu->bdf )
+            return is_hardware_domain(pdev->domain) ? 0 : -ENODEV;
+
     iommu = find_iommu_for_device(pdev->seg, bdf);
     if ( unlikely(!iommu) )
     {