Re: [PATCH v5 4/6] powerpc/pseries: Consolidate different NUMA distance update code paths

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

David Gibson <david@gibson.dropbear.id.au> writes:

> On Thu, Jul 22, 2021 at 12:37:46PM +0530, Aneesh Kumar K.V wrote:
>> David Gibson <david@gibson.dropbear.id.au> writes:
>> 
>> > On Mon, Jun 28, 2021 at 08:41:15PM +0530, Aneesh Kumar K.V wrote:

....

> 
>> >
>> >> +		nid = of_read_number(&aa.arrays[index], 1);
>> >> +
>> >> +		if (nid == 0xffff || nid >= nr_node_ids)
>> >> +			nid = default_nid;
>> >> +		if (nid > 0 && affinity_form == FORM1_AFFINITY) {
>> >> +			int i;
>> >> +			const __be32 *associativity;
>> >> +
>> >> +			index = lmb->aa_index * aa.array_sz;
>> >> +			associativity = &aa.arrays[index];
>> >> +			/*
>> >> +			 * lookup array associativity entries have different format
>> >> +			 * There is no length of the array as the first element.
>> >
>> > The difference it very small, and this is not a hot path.  Couldn't
>> > you reduce a chunk of code by prepending aa.array_sz, then re-using
>> > __initialize_form1_numa_distance.  Or even making
>> > __initialize_form1_numa_distance() take the length as a parameter.
>> 
>> The changes are small but confusing w.r.t how we look at the
>> associativity-lookup-arrays. The way we interpret associativity array
>> and associativity lookup array using primary_domain_index is different.
>> Hence the '-1' in the node lookup here.
>
> They're really not, though.  It's exactly the same interpretation of
> the associativity array itself - it's just that one of them has the
> array prepended with a (redundant) length.  So you can make
> __initialize_form1_numa_distance() work on the "bare" associativity
> array, with a given length.  Here you call it with aa.array_sz as the
> length, and in the other place you call it with prop[0] as the length.
>
>> 
>> 	index = lmb->aa_index * aa.array_sz + primary_domain_index - 1;
>> 	nid = of_read_number(&aa.arrays[index], 1);
>> 
>> 
>> >
>> >> +			 */
>> >> +			for (i = 0; i < max_associativity_domain_index; i++) {
>> >> +				const __be32 *entry;
>> >> +
>> >> +				entry = &associativity[be32_to_cpu(distance_ref_points[i]) - 1];
>> >
>> > Does anywhere verify that distance_ref_points[i] <= aa.array_size for
>> > every i?
>> 
>> We do check for 
>> 
>> 	if (primary_domain_index <= aa.array_sz &&
>
> Right, but that doesn't check the other distance_ref_points entries.
> Not that there's any reason to have extra entries with Form2, but we
> still don't want stray array accesses.

This is how the change looks. I am not convinced this makes it simpler.
I will add that as the last patch and we can drop that if we find that
not helpful? 

modified   arch/powerpc/mm/numa.c
@@ -171,20 +171,31 @@ static void unmap_cpu_from_node(unsigned long cpu)
 }
 #endif /* CONFIG_HOTPLUG_CPU || CONFIG_PPC_SPLPAR */
 
-/*
- * Returns nid in the range [0..nr_node_ids], or -1 if no useful NUMA
- * info is found.
- */
-static int associativity_to_nid(const __be32 *associativity)
+static int __associativity_to_nid(const __be32 *associativity,
+				  bool lookup_array_assoc,
+				  int max_array_index)
 {
 	int nid = NUMA_NO_NODE;
+	int index;
 
 	if (!numa_enabled)
 		goto out;
+	/*
+	 * ibm,associativity-lookup-array doesn't have element
+	 * count at the start of the associativity. Hence
+	 * decrement the primary_domain_index when used with
+	 * lookup-array associativity.
+	 */
+	if (lookup_array_assoc)
+		index = primary_domain_index - 1;
+	else {
+		index = primary_domain_index;
+		max_array_index = of_read_number(associativity, 1);
+	}
+	if (index > max_array_index)
+		goto out;
 
-	if (of_read_number(associativity, 1) >= primary_domain_index)
-		nid = of_read_number(&associativity[primary_domain_index], 1);
-
+	nid = of_read_number(&associativity[index], 1);
 	/* POWER4 LPAR uses 0xffff as invalid node */
 	if (nid == 0xffff || nid >= nr_node_ids)
 		nid = NUMA_NO_NODE;
@@ -192,6 +203,15 @@ static int associativity_to_nid(const __be32 *associativity)
 	return nid;
 }
 
+/*
+ * Returns nid in the range [0..nr_node_ids], or -1 if no useful NUMA
+ * info is found.
+ */
+static inline int associativity_to_nid(const __be32 *associativity)
+{
+	return __associativity_to_nid(associativity, false, 0);
+}
+
 static int __cpu_form2_relative_distance(__be32 *cpu1_assoc, __be32 *cpu2_assoc)
 {
 	int dist;
@@ -295,19 +315,38 @@ int of_node_to_nid(struct device_node *device)
 }
 EXPORT_SYMBOL(of_node_to_nid);
 
-static void __initialize_form1_numa_distance(const __be32 *associativity)
+static void __initialize_form1_numa_distance(const __be32 *associativity,
+					     bool lookup_array_assoc,
+					     int max_array_index)
 {
 	int i, nid;
+	int index_offset = 0;
 
 	if (affinity_form != FORM1_AFFINITY)
 		return;
+	/*
+	 * ibm,associativity-lookup-array doesn't have element
+	 * count at the start of the associativity. Hence
+	 * decrement the distance_ref_points index when used with
+	 * lookup-array associativity.
+	 */
+	if (lookup_array_assoc)
+		index_offset = 1;
+	else
+		max_array_index = of_read_number(associativity, 1);
 
-	nid = associativity_to_nid(associativity);
+	nid = __associativity_to_nid(associativity, lookup_array_assoc, max_array_index);
 	if (nid != NUMA_NO_NODE) {
 		for (i = 0; i < distance_ref_points_depth; i++) {
 			const __be32 *entry;
+			int index = be32_to_cpu(distance_ref_points[i]) - index_offset;
 
-			entry = &associativity[be32_to_cpu(distance_ref_points[i])];
+			/*
+			 * broken hierarchy, return with broken distance table
+			 */
+			if (index > max_array_index)
+				return;
+			entry = &associativity[index];
 			distance_lookup_table[nid][i] = of_read_number(entry, 1);
 		}
 	}
@@ -321,7 +360,7 @@ static void initialize_form1_numa_distance(struct device_node *node)
 	if (!associativity)
 		return;
 
-	__initialize_form1_numa_distance(associativity);
+	__initialize_form1_numa_distance(associativity, false, 0);
 }
 
 /*
@@ -586,27 +625,14 @@ static int get_nid_and_numa_distance(struct drmem_lmb *lmb)
 
 	if (primary_domain_index <= aa.array_sz &&
 	    !(lmb->flags & DRCONF_MEM_AI_INVALID) && lmb->aa_index < aa.n_arrays) {
-		index = lmb->aa_index * aa.array_sz + primary_domain_index - 1;
-		nid = of_read_number(&aa.arrays[index], 1);
+		const __be32 *associativity;
 
-		if (nid == 0xffff || nid >= nr_node_ids)
-			nid = default_nid;
+		index = lmb->aa_index * aa.array_sz;
+		associativity = &aa.arrays[index];
+		nid = __associativity_to_nid(associativity, true, aa.array_sz - 1);
 		if (nid > 0 && affinity_form == FORM1_AFFINITY) {
-			int i;
-			const __be32 *associativity;
-
-			index = lmb->aa_index * aa.array_sz;
-			associativity = &aa.arrays[index];
-			/*
-			 * lookup array associativity entries have different format
-			 * There is no length of the array as the first element.
-			 */
-			for (i = 0; i < distance_ref_points_depth; i++) {
-				const __be32 *entry;
-
-				entry = &associativity[be32_to_cpu(distance_ref_points[i]) - 1];
-				distance_lookup_table[nid][i] = of_read_number(entry, 1);
-			}
+			__initialize_form1_numa_distance(associativity,
+							 true, aa.array_sz - 1);
 		}
 	}
 	return nid;
@@ -632,9 +658,11 @@ int of_drconf_to_nid_single(struct drmem_lmb *lmb)
 
 	if (primary_domain_index <= aa.array_sz &&
 	    !(lmb->flags & DRCONF_MEM_AI_INVALID) && lmb->aa_index < aa.n_arrays) {
-		index = lmb->aa_index * aa.array_sz + primary_domain_index - 1;
-		nid = of_read_number(&aa.arrays[index], 1);
+		const __be32 *associativity;
 
+		index = lmb->aa_index * aa.array_sz;
+		associativity = &aa.arrays[index];
+		nid = __associativity_to_nid(associativity, true, aa.array_sz - 1);
 		if (nid == 0xffff || nid >= nr_node_ids)
 			nid = default_nid;
 	}
@@ -939,7 +967,7 @@ static int __init parse_numa_properties(void)
 
 		if (__vphn_get_associativity(i, vphn_assoc) == 0) {
 			nid = associativity_to_nid(vphn_assoc);
-			__initialize_form1_numa_distance(vphn_assoc);
+			__initialize_form1_numa_distance(vphn_assoc, false, 0);
 		} else {
 
 			/*
@@ -953,7 +981,7 @@ static int __init parse_numa_properties(void)
 			associativity = of_get_associativity(cpu);
 			if (associativity) {
 				nid = associativity_to_nid(associativity);
-				__initialize_form1_numa_distance(associativity);
+				__initialize_form1_numa_distance(associativity, false, 0);
 			}
 			of_node_put(cpu);
 		}
@@ -993,7 +1021,7 @@ static int __init parse_numa_properties(void)
 		associativity = of_get_associativity(memory);
 		if (associativity) {
 			nid = associativity_to_nid(associativity);
-			__initialize_form1_numa_distance(associativity);
+			__initialize_form1_numa_distance(associativity, false, 0);
 		} else
 			nid = default_nid;