bpf: Add dmabuf iterator

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>
Link: https://lore.kernel.org/r/20250522230429.941193-3-tjmercier@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 105 insertions, 0 deletions

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);