KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 394 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..e46fe5c32
--- /dev/null
+++ b/drivers/base/regmap/regcache-maple.c
@@ -0,0 +1,394 @@
+// 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 = 0, upper_last = 0;
+	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 void 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;
+
+	mas_lock(&mas);
+	mas_for_each(&mas, entry, UINT_MAX)
+		kfree(entry);
+	__mt_destroy(mt);
+	mas_unlock(&mas);
+
+	kfree(mt);
+	map->cache = NULL;
+}
+
+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,
+};