AMD/IOMMU: introduce a "valid" flag for IVRS mappings

For us to no longer blindly allocate interrupt remapping tables for
everything the ACPI tables name, we can't use struct ivrs_mappings'
intremap_table field anymore to also have the meaning of "this entry
is valid". Add a separate boolean field instead.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v5: New.

--- a/xen/drivers/passthrough/amd/iommu_acpi.c
+++ b/xen/drivers/passthrough/amd/iommu_acpi.c
@@ -88,6 +88,8 @@ static void __init add_ivrs_mapping_entr
          }
     }
 
+    ivrs_mappings[alias_id].valid = true;
+
     /* Assign IOMMU hardware. */
     ivrs_mappings[bdf].iommu = iommu;
 }
--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -1244,7 +1244,6 @@ static int __init amd_iommu_setup_device
     u16 seg, struct ivrs_mappings *ivrs_mappings)
 {
     unsigned int bdf;
-    void *intr_tb, *dte;
 
     BUG_ON( (ivrs_bdf_entries == 0) );
 
@@ -1264,16 +1263,17 @@ static int __init amd_iommu_setup_device
     /* Add device table entries */
     for ( bdf = 0; bdf < ivrs_bdf_entries; bdf++ )
     {
-        intr_tb = ivrs_mappings[bdf].intremap_table;
-
-        if ( intr_tb )
+        if ( ivrs_mappings[bdf].valid )
         {
+            void *dte;
+
             /* add device table entry */
             dte = device_table.buffer + (bdf * IOMMU_DEV_TABLE_ENTRY_SIZE);
             iommu_dte_add_device_entry(dte, &ivrs_mappings[bdf]);
 
             amd_iommu_set_intremap_table(
-                dte, (u64)virt_to_maddr(intr_tb), iommu_intremap);
+                dte, virt_to_maddr(ivrs_mappings[bdf].intremap_table),
+                iommu_intremap);
         }
     }
 
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -69,8 +69,8 @@ struct amd_iommu *find_iommu_for_device(
  * table and I/O page table respectively. Such devices will have
  * both alias entry and select entry in IVRS structure.
  *
- * Return original device id, if device has valid interrupt remapping
- * table setup for both select entry and alias entry.
+ * Return original device id if both the specific entry and the alias entry
+ * have been marked valid.
  */
 int get_dma_requestor_id(uint16_t seg, uint16_t bdf)
 {
@@ -79,8 +79,7 @@ int get_dma_requestor_id(uint16_t seg, u
 
     BUG_ON ( bdf >= ivrs_bdf_entries );
     req_id = ivrs_mappings[bdf].dte_requestor_id;
-    if ( (ivrs_mappings[bdf].intremap_table != NULL) &&
-         (ivrs_mappings[req_id].intremap_table != NULL) )
+    if ( ivrs_mappings[bdf].valid && ivrs_mappings[req_id].valid )
         req_id = bdf;
 
     return req_id;
--- a/xen/include/asm-x86/amd-iommu.h
+++ b/xen/include/asm-x86/amd-iommu.h
@@ -111,6 +111,7 @@ struct ivrs_mappings {
     u8 unity_map_enable;
     u8 write_permission;
     u8 read_permission;
+    bool valid;
     unsigned long addr_range_start;
     unsigned long addr_range_length;
     struct amd_iommu *iommu;