This commit introduces the bpf page cache iterator. This iterator allows
users to run a bpf prog against each page in the "page cache".
Internally, the "page cache" is extremely tied to VFS superblock + inode
combo. Because of this, iter_pagecache will only examine pages in the
caller's mount namespace.
Signed-off-by: Daniel Xu <d...@dxuuu.xyz>
---
kernel/bpf/Makefile | 2 +-
kernel/bpf/pagecache_iter.c | 293 ++++++++++++++++++++++++++++++++++++
2 files changed, 294 insertions(+), 1 deletion(-)
create mode 100644 kernel/bpf/pagecache_iter.c
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 7f33098ca63f..3deb6a8d3f75 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -6,7 +6,7 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
endif
CFLAGS_core.o += $(call cc-disable-warning, override-init) $(cflags-nogcse-yy)
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
bpf_iter.o map_iter.o task_iter.o prog_iter.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
bpf_iter.o pagecache_iter.o map_iter.o task_iter.o prog_iter.o
obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o
bpf_lru_list.o lpm_trie.o map_in_map.o
obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o
obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
diff --git a/kernel/bpf/pagecache_iter.c b/kernel/bpf/pagecache_iter.c
new file mode 100644
index 000000000000..8442ab0d4221
--- /dev/null
+++ b/kernel/bpf/pagecache_iter.c
@@ -0,0 +1,293 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2021 Facebook */
+
+#include <linux/bpf.h>
+#include <linux/btf_ids.h>
+#include <linux/init.h>
+#include <linux/mm_types.h>
+#include <linux/mnt_namespace.h>
+#include <linux/nsproxy.h>
+#include <linux/pagemap.h>
+#include <linux/radix-tree.h>
+#include <linux/seq_file.h>
+#include "../../fs/mount.h"
+
+struct bpf_iter_seq_pagecache_info {
+ struct mnt_namespace *ns;
+ struct radix_tree_root superblocks;
+ struct super_block *cur_sb;
+ struct inode *cur_inode;
+ unsigned long cur_page_idx;
+};
+
+static struct super_block *goto_next_sb(struct bpf_iter_seq_pagecache_info
*info)
+{
+ struct super_block *sb = NULL;
+ struct radix_tree_iter iter;
+ void **slot;
+
+ radix_tree_for_each_slot(slot, &info->superblocks, &iter,
+ ((unsigned long)info->cur_sb + 1)) {
+ sb = (struct super_block *)iter.index;
+ break;
+ }
+
+ info->cur_sb = sb;
+ info->cur_inode = NULL;
+ info->cur_page_idx = 0;
+ return sb;
+}
+
+static bool inode_unusual(struct inode *inode) {
+ return ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
+ (inode->i_mapping->nrpages == 0));
+}
+
+static struct inode *goto_next_inode(struct bpf_iter_seq_pagecache_info *info)
+{
+ struct inode *prev_inode = info->cur_inode;
+ struct inode *inode;
+
+retry:
+ BUG_ON(!info->cur_sb);
+ spin_lock(&info->cur_sb->s_inode_list_lock);
+
+ if (!info->cur_inode) {
+ list_for_each_entry(inode, &info->cur_sb->s_inodes, i_sb_list) {
+ spin_lock(&inode->i_lock);
+ if (inode_unusual(inode)) {
+ spin_unlock(&inode->i_lock);
+ continue;
+ }
+ __iget(inode);
+ spin_unlock(&inode->i_lock);
+ info->cur_inode = inode;
+ break;
+ }
+ } else {
+ inode = info->cur_inode;
+ info->cur_inode = NULL;
+ list_for_each_entry_continue(inode, &info->cur_sb->s_inodes,
+ i_sb_list) {
+ spin_lock(&inode->i_lock);
+ if (inode_unusual(inode)) {
+ spin_unlock(&inode->i_lock);
+ continue;
+ }
+ __iget(inode);
+ spin_unlock(&inode->i_lock);
+ info->cur_inode = inode;
+ break;
+ }
+ }
+
+ /* Seen all inodes in this superblock */
+ if (!info->cur_inode) {
+ spin_unlock(&info->cur_sb->s_inode_list_lock);
+ if (!goto_next_sb(info)) {
+ inode = NULL;
+ goto out;
+ }
+
+ goto retry;
+ }
+
+ spin_unlock(&info->cur_sb->s_inode_list_lock);
+ info->cur_page_idx = 0;
+out:
+ iput(prev_inode);
+ return info->cur_inode;
+}
+
+static struct page *goto_next_page(struct bpf_iter_seq_pagecache_info *info)
+{
+ struct page *page, *ret = NULL;
+ unsigned long idx;
+
+ rcu_read_lock();
+retry:
+ BUG_ON(!info->cur_inode);
+ ret = NULL;
+ xa_for_each_start(&info->cur_inode->i_data.i_pages, idx, page,
+ info->cur_page_idx) {
+ if (!page_cache_get_speculative(page))
+ continue;
+
+ ret = page;
+ info->cur_page_idx = idx + 1;
+ break;
+ }
+
+ if (!ret) {
+ /* Seen all inodes and superblocks */
+ if (!goto_next_inode(info))
+ goto out;
+
+ goto retry;
+ }
+
+out:
+ rcu_read_unlock();
+ return ret;
+}
+
+static void *pagecache_seq_start(struct seq_file *seq, loff_t *pos)
+{
+ struct bpf_iter_seq_pagecache_info *info = seq->private;
+ struct page *page;
+
+ if (!info->cur_sb && !goto_next_sb(info))
+ return NULL;
+ if (!info->cur_inode && !goto_next_inode(info))
+ return NULL;
+
+ page = goto_next_page(info);
+ if (!page)
+ return NULL;
+
+ if (*pos == 0)
+ ++*pos;
+
+ return page;
+
+}
+
+static void *pagecache_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+ struct bpf_iter_seq_pagecache_info *info = seq->private;
+ struct page *page;
+
+ ++*pos;
+ put_page((struct page *)v);
+ page = goto_next_page(info);
+ if (!page)
+ return NULL;
+
+ return page;
+}
+
+struct bpf_iter__pagecache {
+ __bpf_md_ptr(struct bpf_iter_meta *, meta);
+ __bpf_md_ptr(struct page *, page);
+};
+
+DEFINE_BPF_ITER_FUNC(pagecache, struct bpf_iter_meta *meta, struct page *page)
+
+static int __pagecache_seq_show(struct seq_file *seq, struct page *page,
+ bool in_stop)
+{
+ struct bpf_iter_meta meta;
+ struct bpf_iter__pagecache ctx;
+ struct bpf_prog *prog;
+
+ meta.seq = seq;
+ prog = bpf_iter_get_info(&meta, in_stop);
+ if (!prog)
+ return 0;
+
+ meta.seq = seq;
+ ctx.meta = &meta;
+ ctx.page = page;
+ return bpf_iter_run_prog(prog, &ctx);
+}
+
+static int pagecache_seq_show(struct seq_file *seq, void *v)
+{
+ return __pagecache_seq_show(seq, v, false);
+}
+
+static void pagecache_seq_stop(struct seq_file *seq, void *v)
+{
+ (void)__pagecache_seq_show(seq, v, true);
+ if (v)
+ put_page((struct page *)v);
+}
+
+static int init_seq_pagecache(void *priv_data, struct bpf_iter_aux_info *aux)
+{
+ struct bpf_iter_seq_pagecache_info *info = priv_data;
+ struct radix_tree_iter iter;
+ struct super_block *sb;
+ struct mount *mnt;
+ void **slot;
+ int err;
+
+ info->ns = current->nsproxy->mnt_ns;
+ get_mnt_ns(info->ns);
+ INIT_RADIX_TREE(&info->superblocks, GFP_KERNEL);
+
+ spin_lock(&info->ns->ns_lock);
+ list_for_each_entry(mnt, &info->ns->list, mnt_list) {
+ sb = mnt->mnt.mnt_sb;
+
+ /* The same mount may be mounted in multiple places */
+ if (radix_tree_lookup(&info->superblocks, (unsigned long)sb))
+ continue;
+
+ err = radix_tree_insert(&info->superblocks,
+ (unsigned long)sb, (void *)1);
+ if (err)
+ goto out;
+ }
+
+ radix_tree_for_each_slot(slot, &info->superblocks, &iter, 0) {
+ sb = (struct super_block *)iter.index;
+ atomic_inc(&sb->s_active);
+ }
+
+ err = 0;
+out:
+ spin_unlock(&info->ns->ns_lock);
+ return err;
+}
+
+static void fini_seq_pagecache(void *priv_data)
+{
+ struct bpf_iter_seq_pagecache_info *info = priv_data;
+ struct radix_tree_iter iter;
+ struct super_block *sb;
+ void **slot;
+
+ radix_tree_for_each_slot(slot, &info->superblocks, &iter, 0) {
+ sb = (struct super_block *)iter.index;
+ atomic_dec(&sb->s_active);
+ radix_tree_delete(&info->superblocks, iter.index);
+ }
+
+ put_mnt_ns(info->ns);
+}
+
+static const struct seq_operations pagecache_seq_ops = {
+ .start = pagecache_seq_start,
+ .next = pagecache_seq_next,
+ .stop = pagecache_seq_stop,
+ .show = pagecache_seq_show,
+};
+
+static const struct bpf_iter_seq_info pagecache_seq_info = {
+ .seq_ops = &pagecache_seq_ops,
+ .init_seq_private = init_seq_pagecache,
+ .fini_seq_private = fini_seq_pagecache,
+ .seq_priv_size = sizeof(struct bpf_iter_seq_pagecache_info),
+};
+
+static struct bpf_iter_reg pagecache_reg_info = {
+ .target = "pagecache",
+ .ctx_arg_info_size = 1,
+ .ctx_arg_info = {
+ { offsetof(struct bpf_iter__pagecache, page),
+ PTR_TO_BTF_ID_OR_NULL },
+ },
+ .seq_info = &pagecache_seq_info,
+};
+
+BTF_ID_LIST(btf_page_id)
+BTF_ID(struct, page)
+
+static int __init bpf_pagecache_iter_init(void)
+{
+ pagecache_reg_info.ctx_arg_info[0].btf_id = *btf_page_id;
+ return bpf_iter_reg_target(&pagecache_reg_info);
+}
+
+late_initcall(bpf_pagecache_iter_init);
--
2.26.3
