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1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
3#include <linux/interval_tree_generic.h>
4#include <linux/slab.h>
5#include <linux/bpf.h>
6#include "range_tree.h"
7
8/*
9 * struct range_tree is a data structure used to allocate contiguous memory
10 * ranges in bpf arena. It's a large bitmap. The contiguous sequence of bits is
11 * represented by struct range_node or 'rn' for short.
12 * rn->rn_rbnode links it into an interval tree while
13 * rn->rb_range_size links it into a second rbtree sorted by size of the range.
14 * __find_range() performs binary search and best fit algorithm to find the
15 * range less or equal requested size.
16 * range_tree_clear/set() clears or sets a range of bits in this bitmap. The
17 * adjacent ranges are merged or split at the same time.
18 *
19 * The split/merge logic is based/borrowed from XFS's xbitmap32 added
20 * in commit 6772fcc8890a ("xfs: convert xbitmap to interval tree").
21 *
22 * The implementation relies on external lock to protect rbtree-s.
23 * The alloc/free of range_node-s is done via kmalloc_nolock().
24 *
25 * bpf arena is using range_tree to represent unallocated slots.
26 * At init time:
27 * range_tree_set(rt, 0, max);
28 * Then:
29 * start = range_tree_find(rt, len);
30 * if (start >= 0)
31 * range_tree_clear(rt, start, len);
32 * to find free range and mark slots as allocated and later:
33 * range_tree_set(rt, start, len);
34 * to mark as unallocated after use.
35 */
36struct range_node {
37 struct rb_node rn_rbnode;
38 struct rb_node rb_range_size;
39 u32 rn_start;
40 u32 rn_last; /* inclusive */
41 u32 __rn_subtree_last;
42};
43
44static struct range_node *rb_to_range_node(struct rb_node *rb)
45{
46 return rb_entry(rb, struct range_node, rb_range_size);
47}
48
49static u32 rn_size(struct range_node *rn)
50{
51 return rn->rn_last - rn->rn_start + 1;
52}
53
54/* Find range that fits best to requested size */
55static inline struct range_node *__find_range(struct range_tree *rt, u32 len)
56{
57 struct rb_node *rb = rt->range_size_root.rb_root.rb_node;
58 struct range_node *best = NULL;
59
60 while (rb) {
61 struct range_node *rn = rb_to_range_node(rb);
62
63 if (len <= rn_size(rn)) {
64 best = rn;
65 rb = rb->rb_right;
66 } else {
67 rb = rb->rb_left;
68 }
69 }
70
71 return best;
72}
73
74s64 range_tree_find(struct range_tree *rt, u32 len)
75{
76 struct range_node *rn;
77
78 rn = __find_range(rt, len);
79 if (!rn)
80 return -ENOENT;
81 return rn->rn_start;
82}
83
84/* Insert the range into rbtree sorted by the range size */
85static inline void __range_size_insert(struct range_node *rn,
86 struct rb_root_cached *root)
87{
88 struct rb_node **link = &root->rb_root.rb_node, *rb = NULL;
89 u64 size = rn_size(rn);
90 bool leftmost = true;
91
92 while (*link) {
93 rb = *link;
94 if (size > rn_size(rb_to_range_node(rb))) {
95 link = &rb->rb_left;
96 } else {
97 link = &rb->rb_right;
98 leftmost = false;
99 }
100 }
101
102 rb_link_node(&rn->rb_range_size, rb, link);
103 rb_insert_color_cached(&rn->rb_range_size, root, leftmost);
104}
105
106#define START(node) ((node)->rn_start)
107#define LAST(node) ((node)->rn_last)
108
109INTERVAL_TREE_DEFINE(struct range_node, rn_rbnode, u32,
110 __rn_subtree_last, START, LAST,
111 static inline __maybe_unused,
112 __range_it)
113
114static inline __maybe_unused void
115range_it_insert(struct range_node *rn, struct range_tree *rt)
116{
117 __range_size_insert(rn, &rt->range_size_root);
118 __range_it_insert(rn, &rt->it_root);
119}
120
121static inline __maybe_unused void
122range_it_remove(struct range_node *rn, struct range_tree *rt)
123{
124 rb_erase_cached(&rn->rb_range_size, &rt->range_size_root);
125 RB_CLEAR_NODE(&rn->rb_range_size);
126 __range_it_remove(rn, &rt->it_root);
127}
128
129static inline __maybe_unused struct range_node *
130range_it_iter_first(struct range_tree *rt, u32 start, u32 last)
131{
132 return __range_it_iter_first(&rt->it_root, start, last);
133}
134
135/* Clear the range in this range tree */
136int range_tree_clear(struct range_tree *rt, u32 start, u32 len)
137{
138 u32 last = start + len - 1;
139 struct range_node *new_rn;
140 struct range_node *rn;
141
142 while ((rn = range_it_iter_first(rt, start, last))) {
143 if (rn->rn_start < start && rn->rn_last > last) {
144 u32 old_last = rn->rn_last;
145
146 /* Overlaps with the entire clearing range */
147 range_it_remove(rn, rt);
148 rn->rn_last = start - 1;
149 range_it_insert(rn, rt);
150
151 /* Add a range */
152 new_rn = kmalloc_nolock(sizeof(struct range_node), __GFP_ACCOUNT,
153 NUMA_NO_NODE);
154 if (!new_rn)
155 return -ENOMEM;
156 new_rn->rn_start = last + 1;
157 new_rn->rn_last = old_last;
158 range_it_insert(new_rn, rt);
159 } else if (rn->rn_start < start) {
160 /* Overlaps with the left side of the clearing range */
161 range_it_remove(rn, rt);
162 rn->rn_last = start - 1;
163 range_it_insert(rn, rt);
164 } else if (rn->rn_last > last) {
165 /* Overlaps with the right side of the clearing range */
166 range_it_remove(rn, rt);
167 rn->rn_start = last + 1;
168 range_it_insert(rn, rt);
169 break;
170 } else {
171 /* in the middle of the clearing range */
172 range_it_remove(rn, rt);
173 kfree_nolock(rn);
174 }
175 }
176 return 0;
177}
178
179/* Is the whole range set ? */
180int is_range_tree_set(struct range_tree *rt, u32 start, u32 len)
181{
182 u32 last = start + len - 1;
183 struct range_node *left;
184
185 /* Is this whole range set ? */
186 left = range_it_iter_first(rt, start, last);
187 if (left && left->rn_start <= start && left->rn_last >= last)
188 return 0;
189 return -ESRCH;
190}
191
192/* Set the range in this range tree */
193int range_tree_set(struct range_tree *rt, u32 start, u32 len)
194{
195 u32 last = start + len - 1;
196 struct range_node *right;
197 struct range_node *left;
198 int err;
199
200 /* Is this whole range already set ? */
201 left = range_it_iter_first(rt, start, last);
202 if (left && left->rn_start <= start && left->rn_last >= last)
203 return 0;
204
205 /* Clear out everything in the range we want to set. */
206 err = range_tree_clear(rt, start, len);
207 if (err)
208 return err;
209
210 /* Do we have a left-adjacent range ? */
211 left = range_it_iter_first(rt, start - 1, start - 1);
212 if (left && left->rn_last + 1 != start)
213 return -EFAULT;
214
215 /* Do we have a right-adjacent range ? */
216 right = range_it_iter_first(rt, last + 1, last + 1);
217 if (right && right->rn_start != last + 1)
218 return -EFAULT;
219
220 if (left && right) {
221 /* Combine left and right adjacent ranges */
222 range_it_remove(left, rt);
223 range_it_remove(right, rt);
224 left->rn_last = right->rn_last;
225 range_it_insert(left, rt);
226 kfree_nolock(right);
227 } else if (left) {
228 /* Combine with the left range */
229 range_it_remove(left, rt);
230 left->rn_last = last;
231 range_it_insert(left, rt);
232 } else if (right) {
233 /* Combine with the right range */
234 range_it_remove(right, rt);
235 right->rn_start = start;
236 range_it_insert(right, rt);
237 } else {
238 left = kmalloc_nolock(sizeof(struct range_node), __GFP_ACCOUNT, NUMA_NO_NODE);
239 if (!left)
240 return -ENOMEM;
241 left->rn_start = start;
242 left->rn_last = last;
243 range_it_insert(left, rt);
244 }
245 return 0;
246}
247
248void range_tree_destroy(struct range_tree *rt)
249{
250 struct range_node *rn;
251
252 while ((rn = range_it_iter_first(rt, 0, -1U))) {
253 range_it_remove(rn, rt);
254 kfree_nolock(rn);
255 }
256}
257
258void range_tree_init(struct range_tree *rt)
259{
260 rt->it_root = RB_ROOT_CACHED;
261 rt->range_size_root = RB_ROOT_CACHED;
262}