The dmabuf iterator traverses the list of all DMA buffers.
DMA buffers are refcounted through their associated struct file. A reference is taken on each buffer as the list is iterated to ensure each buffer persists for the duration of the bpf program execution without holding the list mutex.
Signed-off-by: T.J. Mercier tjmercier@google.com Reviewed-by: Christian König christian.koenig@amd.com Acked-by: Song Liu song@kernel.org --- drivers/dma-buf/dma-buf.c | 68 +++++++++++++++++++++++++ include/linux/dma-buf.h | 2 + kernel/bpf/Makefile | 3 ++ kernel/bpf/dmabuf_iter.c | 102 ++++++++++++++++++++++++++++++++++++++ 4 files changed, 175 insertions(+) create mode 100644 kernel/bpf/dmabuf_iter.c
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 8d151784e302..6b59506a1b94 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -19,7 +19,9 @@ #include <linux/anon_inodes.h> #include <linux/export.h> #include <linux/debugfs.h> +#include <linux/list.h> #include <linux/module.h> +#include <linux/mutex.h> #include <linux/seq_file.h> #include <linux/sync_file.h> #include <linux/poll.h> @@ -55,6 +57,72 @@ static void __dma_buf_list_del(struct dma_buf *dmabuf) mutex_unlock(&dmabuf_list_mutex); }
+/** + * dma_buf_iter_begin - begin iteration through global list of all DMA buffers + * + * Returns the first buffer in the global list of DMA-bufs that's not in the + * process of being destroyed. Increments that buffer's reference count to + * prevent buffer destruction. Callers must release the reference, either by + * continuing iteration with dma_buf_iter_next(), or with dma_buf_put(). + * + * Return: + * * First buffer from global list, with refcount elevated + * * NULL if no active buffers are present + */ +struct dma_buf *dma_buf_iter_begin(void) +{ + struct dma_buf *ret = NULL, *dmabuf; + + /* + * The list mutex does not protect a dmabuf's refcount, so it can be + * zeroed while we are iterating. We cannot call get_dma_buf() since the + * caller may not already own a reference to the buffer. + */ + mutex_lock(&dmabuf_list_mutex); + list_for_each_entry(dmabuf, &dmabuf_list, list_node) { + if (file_ref_get(&dmabuf->file->f_ref)) { + ret = dmabuf; + break; + } + } + mutex_unlock(&dmabuf_list_mutex); + return ret; +} + +/** + * dma_buf_iter_next - continue iteration through global list of all DMA buffers + * @dmabuf: [in] pointer to dma_buf + * + * Decrements the reference count on the provided buffer. Returns the next + * buffer from the remainder of the global list of DMA-bufs with its reference + * count incremented. Callers must release the reference, either by continuing + * iteration with dma_buf_iter_next(), or with dma_buf_put(). + * + * Return: + * * Next buffer from global list, with refcount elevated + * * NULL if no additional active buffers are present + */ +struct dma_buf *dma_buf_iter_next(struct dma_buf *dmabuf) +{ + struct dma_buf *ret = NULL; + + /* + * The list mutex does not protect a dmabuf's refcount, so it can be + * zeroed while we are iterating. We cannot call get_dma_buf() since the + * caller may not already own a reference to the buffer. + */ + mutex_lock(&dmabuf_list_mutex); + dma_buf_put(dmabuf); + list_for_each_entry_continue(dmabuf, &dmabuf_list, list_node) { + if (file_ref_get(&dmabuf->file->f_ref)) { + ret = dmabuf; + break; + } + } + mutex_unlock(&dmabuf_list_mutex); + return ret; +} + static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen) { struct dma_buf *dmabuf; diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 8ff4add71f88..7af2ea839f58 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -634,4 +634,6 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map); void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map); int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map); void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map); +struct dma_buf *dma_buf_iter_begin(void); +struct dma_buf *dma_buf_iter_next(struct dma_buf *dmbuf); #endif /* __DMA_BUF_H__ */ diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile index 70502f038b92..3a335c50e6e3 100644 --- a/kernel/bpf/Makefile +++ b/kernel/bpf/Makefile @@ -53,6 +53,9 @@ obj-$(CONFIG_BPF_SYSCALL) += relo_core.o obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o +ifeq ($(CONFIG_DMA_SHARED_BUFFER),y) +obj-$(CONFIG_BPF_SYSCALL) += dmabuf_iter.o +endif
CFLAGS_REMOVE_percpu_freelist.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_bpf_lru_list.o = $(CC_FLAGS_FTRACE) diff --git a/kernel/bpf/dmabuf_iter.c b/kernel/bpf/dmabuf_iter.c new file mode 100644 index 000000000000..83ef54d78b62 --- /dev/null +++ b/kernel/bpf/dmabuf_iter.c @@ -0,0 +1,102 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright (c) 2025 Google LLC */ +#include <linux/bpf.h> +#include <linux/btf_ids.h> +#include <linux/dma-buf.h> +#include <linux/kernel.h> +#include <linux/seq_file.h> + +static void *dmabuf_iter_seq_start(struct seq_file *seq, loff_t *pos) +{ + if (*pos) + return NULL; + + return dma_buf_iter_begin(); +} + +static void *dmabuf_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + struct dma_buf *dmabuf = v; + + ++*pos; + + return dma_buf_iter_next(dmabuf); +} + +struct bpf_iter__dmabuf { + __bpf_md_ptr(struct bpf_iter_meta *, meta); + __bpf_md_ptr(struct dma_buf *, dmabuf); +}; + +static int __dmabuf_seq_show(struct seq_file *seq, void *v, bool in_stop) +{ + struct bpf_iter_meta meta = { + .seq = seq, + }; + struct bpf_iter__dmabuf ctx = { + .meta = &meta, + .dmabuf = v, + }; + struct bpf_prog *prog = bpf_iter_get_info(&meta, in_stop); + + if (prog) + return bpf_iter_run_prog(prog, &ctx); + + return 0; +} + +static int dmabuf_iter_seq_show(struct seq_file *seq, void *v) +{ + return __dmabuf_seq_show(seq, v, false); +} + +static void dmabuf_iter_seq_stop(struct seq_file *seq, void *v) +{ + struct dma_buf *dmabuf = v; + + if (dmabuf) + dma_buf_put(dmabuf); +} + +static const struct seq_operations dmabuf_iter_seq_ops = { + .start = dmabuf_iter_seq_start, + .next = dmabuf_iter_seq_next, + .stop = dmabuf_iter_seq_stop, + .show = dmabuf_iter_seq_show, +}; + +static void bpf_iter_dmabuf_show_fdinfo(const struct bpf_iter_aux_info *aux, + struct seq_file *seq) +{ + seq_puts(seq, "dmabuf iter\n"); +} + +static const struct bpf_iter_seq_info dmabuf_iter_seq_info = { + .seq_ops = &dmabuf_iter_seq_ops, + .init_seq_private = NULL, + .fini_seq_private = NULL, + .seq_priv_size = 0, +}; + +static struct bpf_iter_reg bpf_dmabuf_reg_info = { + .target = "dmabuf", + .feature = BPF_ITER_RESCHED, + .show_fdinfo = bpf_iter_dmabuf_show_fdinfo, + .ctx_arg_info_size = 1, + .ctx_arg_info = { + { offsetof(struct bpf_iter__dmabuf, dmabuf), + PTR_TO_BTF_ID_OR_NULL }, + }, + .seq_info = &dmabuf_iter_seq_info, +}; + +DEFINE_BPF_ITER_FUNC(dmabuf, struct bpf_iter_meta *meta, struct dma_buf *dmabuf) +BTF_ID_LIST_SINGLE(bpf_dmabuf_btf_id, struct, dma_buf) + +static int __init dmabuf_iter_init(void) +{ + bpf_dmabuf_reg_info.ctx_arg_info[0].btf_id = bpf_dmabuf_btf_id[0]; + return bpf_iter_reg_target(&bpf_dmabuf_reg_info); +} + +late_initcall(dmabuf_iter_init);