1 files changed, 272 insertions, 0 deletions
diff --git a/kernel/bpf/range_tree.c b/kernel/bpf/range_tree.c
new file mode 100644
index 000000000000..5bdf9aadca3a
--- /dev/null
+++ b/kernel/bpf/range_tree.c
@@ -0,0 +1,272 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <linux/interval_tree_generic.h>
+#include <linux/slab.h>
+#include <linux/bpf_mem_alloc.h>
+#include <linux/bpf.h>
+#include "range_tree.h"
+
+/*
+ * struct range_tree is a data structure used to allocate contiguous memory
+ * ranges in bpf arena. It's a large bitmap. The contiguous sequence of bits is
+ * represented by struct range_node or 'rn' for short.
+ * rn->rn_rbnode links it into an interval tree while
+ * rn->rb_range_size links it into a second rbtree sorted by size of the range.
+ * __find_range() performs binary search and best fit algorithm to find the
+ * range less or equal requested size.
+ * range_tree_clear/set() clears or sets a range of bits in this bitmap. The
+ * adjacent ranges are merged or split at the same time.
+ *
+ * The split/merge logic is based/borrowed from XFS's xbitmap32 added
+ * in commit 6772fcc8890a ("xfs: convert xbitmap to interval tree").
+ *
+ * The implementation relies on external lock to protect rbtree-s.
+ * The alloc/free of range_node-s is done via bpf_mem_alloc.
+ *
+ * bpf arena is using range_tree to represent unallocated slots.
+ * At init time:
+ *   range_tree_set(rt, 0, max);
+ * Then:
+ *   start = range_tree_find(rt, len);
+ *   if (start >= 0)
+ *     range_tree_clear(rt, start, len);
+ * to find free range and mark slots as allocated and later:
+ *   range_tree_set(rt, start, len);
+ * to mark as unallocated after use.
+ */
+struct range_node {
+	struct rb_node rn_rbnode;
+	struct rb_node rb_range_size;
+	u32 rn_start;
+	u32 rn_last; /* inclusive */
+	u32 __rn_subtree_last;
+};
+
+static struct range_node *rb_to_range_node(struct rb_node *rb)
+{
+	return rb_entry(rb, struct range_node, rb_range_size);
+}
+
+static u32 rn_size(struct range_node *rn)
+{
+	return rn->rn_last - rn->rn_start + 1;
+}
+
+/* Find range that fits best to requested size */
+static inline struct range_node *__find_range(struct range_tree *rt, u32 len)
+{
+	struct rb_node *rb = rt->range_size_root.rb_root.rb_node;
+	struct range_node *best = NULL;
+
+	while (rb) {
+		struct range_node *rn = rb_to_range_node(rb);
+
+		if (len <= rn_size(rn)) {
+			best = rn;
+			rb = rb->rb_right;
+		} else {
+			rb = rb->rb_left;
+		}
+	}
+
+	return best;
+}
+
+s64 range_tree_find(struct range_tree *rt, u32 len)
+{
+	struct range_node *rn;
+
+	rn = __find_range(rt, len);
+	if (!rn)
+		return -ENOENT;
+	return rn->rn_start;
+}
+
+/* Insert the range into rbtree sorted by the range size */
+static inline void __range_size_insert(struct range_node *rn,
+				       struct rb_root_cached *root)
+{
+	struct rb_node **link = &root->rb_root.rb_node, *rb = NULL;
+	u64 size = rn_size(rn);
+	bool leftmost = true;
+
+	while (*link) {
+		rb = *link;
+		if (size > rn_size(rb_to_range_node(rb))) {
+			link = &rb->rb_left;
+		} else {
+			link = &rb->rb_right;
+			leftmost = false;
+		}
+	}
+
+	rb_link_node(&rn->rb_range_size, rb, link);
+	rb_insert_color_cached(&rn->rb_range_size, root, leftmost);
+}
+
+#define START(node) ((node)->rn_start)
+#define LAST(node)  ((node)->rn_last)
+
+INTERVAL_TREE_DEFINE(struct range_node, rn_rbnode, u32,
+		     __rn_subtree_last, START, LAST,
+		     static inline __maybe_unused,
+		     __range_it)
+
+static inline __maybe_unused void
+range_it_insert(struct range_node *rn, struct range_tree *rt)
+{
+	__range_size_insert(rn, &rt->range_size_root);
+	__range_it_insert(rn, &rt->it_root);
+}
+
+static inline __maybe_unused void
+range_it_remove(struct range_node *rn, struct range_tree *rt)
+{
+	rb_erase_cached(&rn->rb_range_size, &rt->range_size_root);
+	RB_CLEAR_NODE(&rn->rb_range_size);
+	__range_it_remove(rn, &rt->it_root);
+}
+
+static inline __maybe_unused struct range_node *
+range_it_iter_first(struct range_tree *rt, u32 start, u32 last)
+{
+	return __range_it_iter_first(&rt->it_root, start, last);
+}
+
+/* Clear the range in this range tree */
+int range_tree_clear(struct range_tree *rt, u32 start, u32 len)
+{
+	u32 last = start + len - 1;
+	struct range_node *new_rn;
+	struct range_node *rn;
+
+	while ((rn = range_it_iter_first(rt, start, last))) {
+		if (rn->rn_start < start && rn->rn_last > last) {
+			u32 old_last = rn->rn_last;
+
+			/* Overlaps with the entire clearing range */
+			range_it_remove(rn, rt);
+			rn->rn_last = start - 1;
+			range_it_insert(rn, rt);
+
+			/* Add a range */
+			migrate_disable();
+			new_rn = bpf_mem_alloc(&bpf_global_ma, sizeof(struct range_node));
+			migrate_enable();
+			if (!new_rn)
+				return -ENOMEM;
+			new_rn->rn_start = last + 1;
+			new_rn->rn_last = old_last;
+			range_it_insert(new_rn, rt);
+		} else if (rn->rn_start < start) {
+			/* Overlaps with the left side of the clearing range */
+			range_it_remove(rn, rt);
+			rn->rn_last = start - 1;
+			range_it_insert(rn, rt);
+		} else if (rn->rn_last > last) {
+			/* Overlaps with the right side of the clearing range */
+			range_it_remove(rn, rt);
+			rn->rn_start = last + 1;
+			range_it_insert(rn, rt);
+			break;
+		} else {
+			/* in the middle of the clearing range */
+			range_it_remove(rn, rt);
+			migrate_disable();
+			bpf_mem_free(&bpf_global_ma, rn);
+			migrate_enable();
+		}
+	}
+	return 0;
+}
+
+/* Is the whole range set ? */
+int is_range_tree_set(struct range_tree *rt, u32 start, u32 len)
+{
+	u32 last = start + len - 1;
+	struct range_node *left;
+
+	/* Is this whole range set ? */
+	left = range_it_iter_first(rt, start, last);
+	if (left && left->rn_start <= start && left->rn_last >= last)
+		return 0;
+	return -ESRCH;
+}
+
+/* Set the range in this range tree */
+int range_tree_set(struct range_tree *rt, u32 start, u32 len)
+{
+	u32 last = start + len - 1;
+	struct range_node *right;
+	struct range_node *left;
+	int err;
+
+	/* Is this whole range already set ? */
+	left = range_it_iter_first(rt, start, last);
+	if (left && left->rn_start <= start && left->rn_last >= last)
+		return 0;
+
+	/* Clear out everything in the range we want to set. */
+	err = range_tree_clear(rt, start, len);
+	if (err)
+		return err;
+
+	/* Do we have a left-adjacent range ? */
+	left = range_it_iter_first(rt, start - 1, start - 1);
+	if (left && left->rn_last + 1 != start)
+		return -EFAULT;
+
+	/* Do we have a right-adjacent range ? */
+	right = range_it_iter_first(rt, last + 1, last + 1);
+	if (right && right->rn_start != last + 1)
+		return -EFAULT;
+
+	if (left && right) {
+		/* Combine left and right adjacent ranges */
+		range_it_remove(left, rt);
+		range_it_remove(right, rt);
+		left->rn_last = right->rn_last;
+		range_it_insert(left, rt);
+		migrate_disable();
+		bpf_mem_free(&bpf_global_ma, right);
+		migrate_enable();
+	} else if (left) {
+		/* Combine with the left range */
+		range_it_remove(left, rt);
+		left->rn_last = last;
+		range_it_insert(left, rt);
+	} else if (right) {
+		/* Combine with the right range */
+		range_it_remove(right, rt);
+		right->rn_start = start;
+		range_it_insert(right, rt);
+	} else {
+		migrate_disable();
+		left = bpf_mem_alloc(&bpf_global_ma, sizeof(struct range_node));
+		migrate_enable();
+		if (!left)
+			return -ENOMEM;
+		left->rn_start = start;
+		left->rn_last = last;
+		range_it_insert(left, rt);
+	}
+	return 0;
+}
+
+void range_tree_destroy(struct range_tree *rt)
+{
+	struct range_node *rn;
+
+	while ((rn = range_it_iter_first(rt, 0, -1U))) {
+		range_it_remove(rn, rt);
+		migrate_disable();
+		bpf_mem_free(&bpf_global_ma, rn);
+		migrate_enable();
+	}
+}
+
+void range_tree_init(struct range_tree *rt)
+{
+	rt->it_root = RB_ROOT_CACHED;
+	rt->range_size_root = RB_ROOT_CACHED;
+}