bpf: Plumb get_unmapped_area() callback into bpf_map_ops

Subsequent patches introduce bpf_arena that imposes special alignment
requirements on address selection.
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20240307031228.42896-4-alexei.starovoitov@gmail.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

include/linux/bpf.h

@@ -139,6 +139,9 @@ struct bpf_map_ops {
 	int (*map_mmap)(struct bpf_map *map, struct vm_area_struct *vma);
 	__poll_t (*map_poll)(struct bpf_map *map, struct file *filp,
 			     struct poll_table_struct *pts);
+	unsigned long (*map_get_unmapped_area)(struct file *filep, unsigned long addr,
+					       unsigned long len, unsigned long pgoff,
+					       unsigned long flags);
 
 	/* Functions called by bpf_local_storage maps */
 	int (*map_local_storage_charge)(struct bpf_local_storage_map *smap,

kernel/bpf/syscall.c

@@ -937,6 +937,21 @@ static __poll_t bpf_map_poll(struct file *filp, struct poll_table_struct *pts)
 	return EPOLLERR;
 }
 
+static unsigned long bpf_get_unmapped_area(struct file *filp, unsigned long addr,
+					   unsigned long len, unsigned long pgoff,
+					   unsigned long flags)
+{
+	struct bpf_map *map = filp->private_data;
+
+	if (map->ops->map_get_unmapped_area)
+		return map->ops->map_get_unmapped_area(filp, addr, len, pgoff, flags);
+#ifdef CONFIG_MMU
+	return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
+#else
+	return addr;
+#endif
+}
+
 const struct file_operations bpf_map_fops = {
 #ifdef CONFIG_PROC_FS
 	.show_fdinfo	= bpf_map_show_fdinfo,
@@ -946,6 +961,7 @@ const struct file_operations bpf_map_fops = {
 	.write		= bpf_dummy_write,
 	.mmap		= bpf_map_mmap,
 	.poll		= bpf_map_poll,
+	.get_unmapped_area = bpf_get_unmapped_area,
 };
 
 int bpf_map_new_fd(struct bpf_map *map, int flags)