1 files changed, 40 insertions, 21 deletions

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index e9cd3fb351..5886192fe3 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -266,6 +266,43 @@ static int iort_idmap_compare(gconstpointer a, gconstpointer b)
     return idmap_a->input_base - idmap_b->input_base;
 }
 
+/* Compute ID ranges (RIDs) from RC that are directed to the ITS Group node */
+static void create_its_idmaps(GArray *its_idmaps, GArray *smmu_idmaps)
+{
+    AcpiIortIdMapping *idmap;
+    AcpiIortIdMapping next_range = {0};
+
+    /*
+     * Based on the RID ranges that are directed to the SMMU, determine the
+     * bypassed RID ranges, i.e., the ones that are directed to the ITS Group
+     * node and do not pass through the SMMU, by subtracting the SMMU-bound
+     * ranges from the full RID range (0x0000–0xFFFF).
+     */
+     for (int i = 0; i < smmu_idmaps->len; i++) {
+        idmap = &g_array_index(smmu_idmaps, AcpiIortIdMapping, i);
+
+        if (next_range.input_base < idmap->input_base) {
+            next_range.id_count = idmap->input_base - next_range.input_base;
+            g_array_append_val(its_idmaps, next_range);
+        }
+
+        next_range.input_base = idmap->input_base + idmap->id_count;
+    }
+
+    /*
+     * Append the last RC -> ITS ID mapping.
+     *
+     * RIDs are 16-bit, according to the PCI Express 2.0 Base Specification, rev
+     * 0.9, section 2.2.6.2, "Transaction Descriptor - Transaction ID Field",
+     * hence the end of the range is 0x10000.
+     */
+    if (next_range.input_base < 0x10000) {
+        next_range.id_count = 0x10000 - next_range.input_base;
+        g_array_append_val(its_idmaps, next_range);
+    }
+}
+
+
 /*
  * Input Output Remapping Table (IORT)
  * Conforms to "IO Remapping Table System Software on ARM Platforms",
@@ -276,7 +313,6 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
 {
     int i, nb_nodes, rc_mapping_count;
     size_t node_size, smmu_offset = 0;
-    AcpiIortIdMapping *idmap;
     uint32_t id = 0;
     GArray *smmu_idmaps = g_array_new(false, true, sizeof(AcpiIortIdMapping));
     GArray *its_idmaps = g_array_new(false, true, sizeof(AcpiIortIdMapping));
@@ -287,8 +323,6 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
     acpi_table_begin(&table, table_data);
 
     if (vms->iommu == VIRT_IOMMU_SMMUV3) {
-        AcpiIortIdMapping next_range = {0};
-
         object_child_foreach_recursive(object_get_root(),
                                        iort_host_bridges, smmu_idmaps);
 
@@ -296,25 +330,10 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
         g_array_sort(smmu_idmaps, iort_idmap_compare);
 
         /*
-         * Split the whole RIDs by mapping from RC to SMMU,
-         * build the ID mapping from RC to ITS directly.
+         * Knowing the ID ranges from the RC to the SMMU, it's possible to
+         * determine the ID ranges from RC that are directed to the ITS.
          */
-        for (i = 0; i < smmu_idmaps->len; i++) {
-            idmap = &g_array_index(smmu_idmaps, AcpiIortIdMapping, i);
-
-            if (next_range.input_base < idmap->input_base) {
-                next_range.id_count = idmap->input_base - next_range.input_base;
-                g_array_append_val(its_idmaps, next_range);
-            }
-
-            next_range.input_base = idmap->input_base + idmap->id_count;
-        }
-
-        /* Append the last RC -> ITS ID mapping */
-        if (next_range.input_base < 0x10000) {
-            next_range.id_count = 0x10000 - next_range.input_base;
-            g_array_append_val(its_idmaps, next_range);
-        }
+        create_its_idmaps(its_idmaps, smmu_idmaps);
 
         nb_nodes = 3; /* RC, ITS, SMMUv3 */
         rc_mapping_count = smmu_idmaps->len + its_idmaps->len;