kernel/bpf/kmem_cache_iter.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Copyright (c) 2024 Google */
   3 #include <linux/bpf.h>
   4 #include <linux/btf_ids.h>
   5 #include <linux/slab.h>
   6 #include <linux/kernel.h>
   7 #include <linux/seq_file.h>
   8
   9 #include "../../mm/slab.h" /* kmem_cache, slab_caches and slab_mutex */
  10
  11 /* open-coded version */
  12 struct bpf_iter_kmem_cache {
  13         __u64 __opaque[1];
  14 } __attribute__((aligned(8)));
  15
  16 struct bpf_iter_kmem_cache_kern {
  17         struct kmem_cache *pos;
  18 } __attribute__((aligned(8)));
  19
  20 #define KMEM_CACHE_POS_START  ((void *)1L)
  21
  22 __bpf_kfunc_start_defs();
  23
  24 __bpf_kfunc int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it)
  25 {
  26         struct bpf_iter_kmem_cache_kern *kit = (void *)it;
  27
  28         BUILD_BUG_ON(sizeof(*kit) > sizeof(*it));
  29         BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it));
  30
  31         kit->pos = KMEM_CACHE_POS_START;
  32         return 0;
  33 }
  34
  35 __bpf_kfunc struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it)
  36 {
  37         struct bpf_iter_kmem_cache_kern *kit = (void *)it;
  38         struct kmem_cache *prev = kit->pos;
  39         struct kmem_cache *next;
  40         bool destroy = false;
  41
  42         if (!prev)
  43                 return NULL;
  44
  45         mutex_lock(&slab_mutex);
  46
  47         if (list_empty(&slab_caches)) {
  48                 mutex_unlock(&slab_mutex);
  49                 return NULL;
  50         }
  51
  52         if (prev == KMEM_CACHE_POS_START)
  53                 next = list_first_entry(&slab_caches, struct kmem_cache, list);
  54         else if (list_last_entry(&slab_caches, struct kmem_cache, list) == prev)
  55                 next = NULL;
  56         else
  57                 next = list_next_entry(prev, list);
  58
  59         /* boot_caches have negative refcount, don't touch them */
  60         if (next && next->refcount > 0)
  61                 next->refcount++;
  62
  63         /* Skip kmem_cache_destroy() for active entries */
  64         if (prev && prev != KMEM_CACHE_POS_START) {
  65                 if (prev->refcount > 1)
  66                         prev->refcount--;
  67                 else if (prev->refcount == 1)
  68                         destroy = true;
  69         }
  70
  71         mutex_unlock(&slab_mutex);
  72
  73         if (destroy)
  74                 kmem_cache_destroy(prev);
  75
  76         kit->pos = next;
  77         return next;
  78 }
  79
  80 __bpf_kfunc void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it)
  81 {
  82         struct bpf_iter_kmem_cache_kern *kit = (void *)it;
  83         struct kmem_cache *s = kit->pos;
  84         bool destroy = false;
  85
  86         if (s == NULL || s == KMEM_CACHE_POS_START)
  87                 return;
  88
  89         mutex_lock(&slab_mutex);
  90
  91         /* Skip kmem_cache_destroy() for active entries */
  92         if (s->refcount > 1)
  93                 s->refcount--;
  94         else if (s->refcount == 1)
  95                 destroy = true;
  96
  97         mutex_unlock(&slab_mutex);
  98
  99         if (destroy)
 100                 kmem_cache_destroy(s);
 101 }
 102
 103 __bpf_kfunc_end_defs();
 104
 105 struct bpf_iter__kmem_cache {
 106         __bpf_md_ptr(struct bpf_iter_meta *, meta);
 107         __bpf_md_ptr(struct kmem_cache *, s);
 108 };
 109
 110 union kmem_cache_iter_priv {
 111         struct bpf_iter_kmem_cache it;
 112         struct bpf_iter_kmem_cache_kern kit;
 113 };
 114
 115 static void *kmem_cache_iter_seq_start(struct seq_file *seq, loff_t *pos)
 116 {
 117         loff_t cnt = 0;
 118         bool found = false;
 119         struct kmem_cache *s;
 120         union kmem_cache_iter_priv *p = seq->private;
 121
 122         mutex_lock(&slab_mutex);
 123
 124         /* Find an entry at the given position in the slab_caches list instead
 125          * of keeping a reference (of the last visited entry, if any) out of
 126          * slab_mutex. It might miss something if one is deleted in the middle
 127          * while it releases the lock.  But it should be rare and there's not
 128          * much we can do about it.
 129          */
 130         list_for_each_entry(s, &slab_caches, list) {
 131                 if (cnt == *pos) {
 132                         /* Make sure this entry remains in the list by getting
 133                          * a new reference count.  Note that boot_cache entries
 134                          * have a negative refcount, so don't touch them.
 135                          */
 136                         if (s->refcount > 0)
 137                                 s->refcount++;
 138                         found = true;
 139                         break;
 140                 }
 141                 cnt++;
 142         }
 143         mutex_unlock(&slab_mutex);
 144
 145         if (!found)
 146                 s = NULL;
 147
 148         p->kit.pos = s;
 149         return s;
 150 }
 151
 152 static void kmem_cache_iter_seq_stop(struct seq_file *seq, void *v)
 153 {
 154         struct bpf_iter_meta meta;
 155         struct bpf_iter__kmem_cache ctx = {
 156                 .meta = &meta,
 157                 .s = v,
 158         };
 159         union kmem_cache_iter_priv *p = seq->private;
 160         struct bpf_prog *prog;
 161
 162         meta.seq = seq;
 163         prog = bpf_iter_get_info(&meta, true);
 164         if (prog && !ctx.s)
 165                 bpf_iter_run_prog(prog, &ctx);
 166
 167         bpf_iter_kmem_cache_destroy(&p->it);
 168 }
 169
 170 static void *kmem_cache_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 171 {
 172         union kmem_cache_iter_priv *p = seq->private;
 173
 174         ++*pos;
 175
 176         return bpf_iter_kmem_cache_next(&p->it);
 177 }
 178
 179 static int kmem_cache_iter_seq_show(struct seq_file *seq, void *v)
 180 {
 181         struct bpf_iter_meta meta;
 182         struct bpf_iter__kmem_cache ctx = {
 183                 .meta = &meta,
 184                 .s = v,
 185         };
 186         struct bpf_prog *prog;
 187         int ret = 0;
 188
 189         meta.seq = seq;
 190         prog = bpf_iter_get_info(&meta, false);
 191         if (prog)
 192                 ret = bpf_iter_run_prog(prog, &ctx);
 193
 194         return ret;
 195 }
 196
 197 static const struct seq_operations kmem_cache_iter_seq_ops = {
 198         .start  = kmem_cache_iter_seq_start,
 199         .next   = kmem_cache_iter_seq_next,
 200         .stop   = kmem_cache_iter_seq_stop,
 201         .show   = kmem_cache_iter_seq_show,
 202 };
 203
 204 BTF_ID_LIST_GLOBAL_SINGLE(bpf_kmem_cache_btf_id, struct, kmem_cache)
 205
 206 static const struct bpf_iter_seq_info kmem_cache_iter_seq_info = {
 207         .seq_ops                = &kmem_cache_iter_seq_ops,
 208         .seq_priv_size          = sizeof(union kmem_cache_iter_priv),
 209 };
 210
 211 static void bpf_iter_kmem_cache_show_fdinfo(const struct bpf_iter_aux_info *aux,
 212                                             struct seq_file *seq)
 213 {
 214         seq_puts(seq, "kmem_cache iter\n");
 215 }
 216
 217 DEFINE_BPF_ITER_FUNC(kmem_cache, struct bpf_iter_meta *meta,
 218                      struct kmem_cache *s)
 219
 220 static struct bpf_iter_reg bpf_kmem_cache_reg_info = {
 221         .target                 = "kmem_cache",
 222         .feature                = BPF_ITER_RESCHED,
 223         .show_fdinfo            = bpf_iter_kmem_cache_show_fdinfo,
 224         .ctx_arg_info_size      = 1,
 225         .ctx_arg_info           = {
 226                 { offsetof(struct bpf_iter__kmem_cache, s),
 227                   PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
 228         },
 229         .seq_info               = &kmem_cache_iter_seq_info,
 230 };
 231
 232 static int __init bpf_kmem_cache_iter_init(void)
 233 {
 234         bpf_kmem_cache_reg_info.ctx_arg_info[0].btf_id = bpf_kmem_cache_btf_id[0];
 235         return bpf_iter_reg_target(&bpf_kmem_cache_reg_info);
 236 }
 237
 238 late_initcall(bpf_kmem_cache_iter_init);