sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 396 insertions, 0 deletions

diff --git a/drivers/base/regmap/regcache-maple.c b/drivers/base/regmap/regcache-maple.c
new file mode 100644
index 000000000..49ba7282e
--- /dev/null
+++ b/drivers/base/regmap/regcache-maple.c
@@ -0,0 +1,396 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Register cache access API - maple tree based cache
+//
+// Copyright 2023 Arm, Ltd
+//
+// Author: Mark Brown <broonie@kernel.org>
+
+#include <linux/debugfs.h>
+#include <linux/device.h>
+#include <linux/maple_tree.h>
+#include <linux/slab.h>
+
+#include "internal.h"
+
+static int regcache_maple_read(struct regmap *map,
+			       unsigned int reg, unsigned int *value)
+{
+	struct maple_tree *mt = map->cache;
+	MA_STATE(mas, mt, reg, reg);
+	unsigned long *entry;
+
+	rcu_read_lock();
+
+	entry = mas_walk(&mas);
+	if (!entry) {
+		rcu_read_unlock();
+		return -ENOENT;
+	}
+
+	*value = entry[reg - mas.index];
+
+	rcu_read_unlock();
+
+	return 0;
+}
+
+static int regcache_maple_write(struct regmap *map, unsigned int reg,
+				unsigned int val)
+{
+	struct maple_tree *mt = map->cache;
+	MA_STATE(mas, mt, reg, reg);
+	unsigned long *entry, *upper, *lower;
+	unsigned long index, last;
+	size_t lower_sz, upper_sz;
+	int ret;
+
+	rcu_read_lock();
+
+	entry = mas_walk(&mas);
+	if (entry) {
+		entry[reg - mas.index] = val;
+		rcu_read_unlock();
+		return 0;
+	}
+
+	/* Any adjacent entries to extend/merge? */
+	mas_set_range(&mas, reg - 1, reg + 1);
+	index = reg;
+	last = reg;
+
+	lower = mas_find(&mas, reg - 1);
+	if (lower) {
+		index = mas.index;
+		lower_sz = (mas.last - mas.index + 1) * sizeof(unsigned long);
+	}
+
+	upper = mas_find(&mas, reg + 1);
+	if (upper) {
+		last = mas.last;
+		upper_sz = (mas.last - mas.index + 1) * sizeof(unsigned long);
+	}
+
+	rcu_read_unlock();
+
+	entry = kmalloc_array(last - index + 1, sizeof(*entry), map->alloc_flags);
+	if (!entry)
+		return -ENOMEM;
+
+	if (lower)
+		memcpy(entry, lower, lower_sz);
+	entry[reg - index] = val;
+	if (upper)
+		memcpy(&entry[reg - index + 1], upper, upper_sz);
+
+	/*
+	 * This is safe because the regmap lock means the Maple lock
+	 * is redundant, but we need to take it due to lockdep asserts
+	 * in the maple tree code.
+	 */
+	mas_lock(&mas);
+
+	mas_set_range(&mas, index, last);
+	ret = mas_store_gfp(&mas, entry, map->alloc_flags);
+
+	mas_unlock(&mas);
+
+	if (ret) {
+		kfree(entry);
+		return ret;
+	}
+	kfree(lower);
+	kfree(upper);
+	return 0;
+}
+
+static int regcache_maple_drop(struct regmap *map, unsigned int min,
+			       unsigned int max)
+{
+	struct maple_tree *mt = map->cache;
+	MA_STATE(mas, mt, min, max);
+	unsigned long *entry, *lower, *upper;
+	/* initialized to work around false-positive -Wuninitialized warning */
+	unsigned long lower_index = 0, lower_last = 0;
+	unsigned long upper_index, upper_last;
+	int ret = 0;
+
+	lower = NULL;
+	upper = NULL;
+
+	mas_lock(&mas);
+
+	mas_for_each(&mas, entry, max) {
+		/*
+		 * This is safe because the regmap lock means the
+		 * Maple lock is redundant, but we need to take it due
+		 * to lockdep asserts in the maple tree code.
+		 */
+		mas_unlock(&mas);
+
+		/* Do we need to save any of this entry? */
+		if (mas.index < min) {
+			lower_index = mas.index;
+			lower_last = min -1;
+
+			lower = kmemdup_array(entry,
+					      min - mas.index, sizeof(*lower),
+					      map->alloc_flags);
+			if (!lower) {
+				ret = -ENOMEM;
+				goto out_unlocked;
+			}
+		}
+
+		if (mas.last > max) {
+			upper_index = max + 1;
+			upper_last = mas.last;
+
+			upper = kmemdup_array(&entry[max - mas.index + 1],
+					      mas.last - max, sizeof(*upper),
+					      map->alloc_flags);
+			if (!upper) {
+				ret = -ENOMEM;
+				goto out_unlocked;
+			}
+		}
+
+		kfree(entry);
+		mas_lock(&mas);
+		mas_erase(&mas);
+
+		/* Insert new nodes with the saved data */
+		if (lower) {
+			mas_set_range(&mas, lower_index, lower_last);
+			ret = mas_store_gfp(&mas, lower, map->alloc_flags);
+			if (ret != 0)
+				goto out;
+			lower = NULL;
+		}
+
+		if (upper) {
+			mas_set_range(&mas, upper_index, upper_last);
+			ret = mas_store_gfp(&mas, upper, map->alloc_flags);
+			if (ret != 0)
+				goto out;
+			upper = NULL;
+		}
+	}
+
+out:
+	mas_unlock(&mas);
+out_unlocked:
+	kfree(lower);
+	kfree(upper);
+
+	return ret;
+}
+
+static int regcache_maple_sync_block(struct regmap *map, unsigned long *entry,
+				     struct ma_state *mas,
+				     unsigned int min, unsigned int max)
+{
+	void *buf;
+	unsigned long r;
+	size_t val_bytes = map->format.val_bytes;
+	int ret = 0;
+
+	mas_pause(mas);
+	rcu_read_unlock();
+
+	/*
+	 * Use a raw write if writing more than one register to a
+	 * device that supports raw writes to reduce transaction
+	 * overheads.
+	 */
+	if (max - min > 1 && regmap_can_raw_write(map)) {
+		buf = kmalloc_array(max - min, val_bytes, map->alloc_flags);
+		if (!buf) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		/* Render the data for a raw write */
+		for (r = min; r < max; r++) {
+			regcache_set_val(map, buf, r - min,
+					 entry[r - mas->index]);
+		}
+
+		ret = _regmap_raw_write(map, min, buf, (max - min) * val_bytes,
+					false);
+
+		kfree(buf);
+	} else {
+		for (r = min; r < max; r++) {
+			ret = _regmap_write(map, r,
+					    entry[r - mas->index]);
+			if (ret != 0)
+				goto out;
+		}
+	}
+
+out:
+	rcu_read_lock();
+
+	return ret;
+}
+
+static int regcache_maple_sync(struct regmap *map, unsigned int min,
+			       unsigned int max)
+{
+	struct maple_tree *mt = map->cache;
+	unsigned long *entry;
+	MA_STATE(mas, mt, min, max);
+	unsigned long lmin = min;
+	unsigned long lmax = max;
+	unsigned int r, v, sync_start;
+	int ret = 0;
+	bool sync_needed = false;
+
+	map->cache_bypass = true;
+
+	rcu_read_lock();
+
+	mas_for_each(&mas, entry, max) {
+		for (r = max(mas.index, lmin); r <= min(mas.last, lmax); r++) {
+			v = entry[r - mas.index];
+
+			if (regcache_reg_needs_sync(map, r, v)) {
+				if (!sync_needed) {
+					sync_start = r;
+					sync_needed = true;
+				}
+				continue;
+			}
+
+			if (!sync_needed)
+				continue;
+
+			ret = regcache_maple_sync_block(map, entry, &mas,
+							sync_start, r);
+			if (ret != 0)
+				goto out;
+			sync_needed = false;
+		}
+
+		if (sync_needed) {
+			ret = regcache_maple_sync_block(map, entry, &mas,
+							sync_start, r);
+			if (ret != 0)
+				goto out;
+			sync_needed = false;
+		}
+	}
+
+out:
+	rcu_read_unlock();
+
+	map->cache_bypass = false;
+
+	return ret;
+}
+
+static int regcache_maple_init(struct regmap *map)
+{
+	struct maple_tree *mt;
+
+	mt = kmalloc_obj(*mt, map->alloc_flags);
+	if (!mt)
+		return -ENOMEM;
+	map->cache = mt;
+
+	mt_init(mt);
+
+	if (!mt_external_lock(mt) && map->lock_key)
+		lockdep_set_class_and_subclass(&mt->ma_lock, map->lock_key, 1);
+
+	return 0;
+}
+
+static int regcache_maple_exit(struct regmap *map)
+{
+	struct maple_tree *mt = map->cache;
+	MA_STATE(mas, mt, 0, UINT_MAX);
+	unsigned int *entry;
+
+	/* if we've already been called then just return */
+	if (!mt)
+		return 0;
+
+	mas_lock(&mas);
+	mas_for_each(&mas, entry, UINT_MAX)
+		kfree(entry);
+	__mt_destroy(mt);
+	mas_unlock(&mas);
+
+	kfree(mt);
+	map->cache = NULL;
+
+	return 0;
+}
+
+static int regcache_maple_insert_block(struct regmap *map, int first,
+					int last)
+{
+	struct maple_tree *mt = map->cache;
+	MA_STATE(mas, mt, first, last);
+	unsigned long *entry;
+	int i, ret;
+
+	entry = kmalloc_array(last - first + 1, sizeof(*entry), map->alloc_flags);
+	if (!entry)
+		return -ENOMEM;
+
+	for (i = 0; i < last - first + 1; i++)
+		entry[i] = map->reg_defaults[first + i].def;
+
+	mas_lock(&mas);
+
+	mas_set_range(&mas, map->reg_defaults[first].reg,
+		      map->reg_defaults[last].reg);
+	ret = mas_store_gfp(&mas, entry, map->alloc_flags);
+
+	mas_unlock(&mas);
+
+	if (ret)
+		kfree(entry);
+
+	return ret;
+}
+
+static int regcache_maple_populate(struct regmap *map)
+{
+	int i;
+	int ret;
+	int range_start;
+
+	range_start = 0;
+
+	/* Scan for ranges of contiguous registers */
+	for (i = 1; i < map->num_reg_defaults; i++) {
+		if (map->reg_defaults[i].reg !=
+		    map->reg_defaults[i - 1].reg + 1) {
+			ret = regcache_maple_insert_block(map, range_start,
+							  i - 1);
+			if (ret != 0)
+				return ret;
+
+			range_start = i;
+		}
+	}
+
+	/* Add the last block */
+	return regcache_maple_insert_block(map, range_start, map->num_reg_defaults - 1);
+}
+
+struct regcache_ops regcache_maple_ops = {
+	.type = REGCACHE_MAPLE,
+	.name = "maple",
+	.init = regcache_maple_init,
+	.exit = regcache_maple_exit,
+	.populate = regcache_maple_populate,
+	.read = regcache_maple_read,
+	.write = regcache_maple_write,
+	.drop = regcache_maple_drop,
+	.sync = regcache_maple_sync,
+};