ACPI / PPTT: Filthy hack to find _a_ backwards reference in the PPTT [ROTTEN]

hulk inclusion
category: feature
bugzilla: 28055
CVE: NA

------------------------------

The alpha MPAM table contains a pointer to the PPTT cache, which it
expects to be unique, which isn't guaranteed.

Ideally we'd take a cache-id, but the hardware doesn't have a
suitable property, instead arm64 will generate an id from the cpu
affinity ids.

To find the cache id we need to find the cacheinfo structure, which
we can do if we have a pptt cpu_node (different to the cache node),
as this is the fw_token used to match the Processor Container that
contains all the CPUs that share this cache.

How can we find the expected-to-be-unique cpu_node from the cache_node?
... add acpi_pptt_find_cache_backwards() to find a PPTT processor node
given a PPTT cache node. This is totally broken as many processor nodes
may point at the same PPTT cache indicating different instances of the
cache. (e.g. all the L1 caches are the same shape, but they aren't the
same cache).

This only works if you cooked your PPTT table to look like this.

Signed-off-by: James Morse <james.morse@arm.com> # ... but its still GPLv2
Signed-off-by: NWang ShaoBo <bobo.shaobowang@huawei.com>
Reviewed-By: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/acpi/pptt.c

@@ -276,6 +276,56 @@ static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_he
 
 	return NULL;
 }
+
+
+/*
+ * acpi_pptt_find_cache_backwards() - Given a PPTT cache find a processor node
+ * that points to it. This lets us find a cacheinfo node by fw_token, but
+ * is totally broken as many processor node may point at the same PPTT
+ * cache indicating different instances of the cache. (e.g. all the L1
+ * caches are the same shape, but they aren't the same cache).
+ * This only works if you cooked your PPTT table to look like this.
+ */
+struct acpi_pptt_processor *
+acpi_pptt_find_cache_backwards(struct acpi_table_header *table_hdr,
+			       struct acpi_pptt_cache *cache)
+{
+	struct acpi_pptt_processor *cpu_node;
+	struct acpi_subtable_header *entry;
+	struct acpi_subtable_header *res;
+	unsigned long table_end;
+	u32 proc_sz;
+	int i;
+
+	table_end = (unsigned long)table_hdr + table_hdr->length;
+	entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
+			     sizeof(struct acpi_table_pptt));
+	proc_sz = sizeof(struct acpi_pptt_processor *);
+
+	/* find the processor structure which points at  with this cpuid */
+	while ((unsigned long)entry + proc_sz < table_end) {
+		if (entry->length == 0) {
+			pr_warn("Invalid zero length subtable\n");
+			break;
+		}
+
+		cpu_node = (struct acpi_pptt_processor *)entry;
+		entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
+				     entry->length);
+
+		if (cpu_node->header.type != ACPI_PPTT_TYPE_PROCESSOR)
+			continue;
+
+		for (i = 0; i < cpu_node->number_of_priv_resources; i++) {
+			res = acpi_get_pptt_resource(table_hdr, cpu_node, i);
+			if (&cache->header == res)
+				return cpu_node;
+		}
+	}
+
+	return NULL;
+}
+
 /**
  * acpi_validate_cache_node() - Given an offset in the table, check this is
  * a cache node.

include/linux/acpi.h

@@ -1323,4 +1323,8 @@ static inline int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
 }
 #endif
 
+struct acpi_pptt_processor *
+acpi_pptt_find_cache_backwards(struct acpi_table_header *table_hdr,
+			       struct acpi_pptt_cache *cache);
+
 #endif	/*_LINUX_ACPI_H*/