Re: [PATCH bpf-next v2 1/4] bpf: Pass arena instead of scratch_page to the pte callbacks

[Emil Tsalapatis]

On Fri Jul 17, 2026 at 7:37 AM EDT, Jiayuan Chen wrote:
> Replace the scratch_page field in the pte-callback data with the arena
> pointer; later patches use other arena fields from these callbacks. No
> functional change.
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>

Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>

> ---
>  kernel/bpf/arena.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
> index 80b7b8a69446..8dbc24460890 100644
> --- a/kernel/bpf/arena.c
> +++ b/kernel/bpf/arena.c
> @@ -143,14 +143,14 @@ static long compute_pgoff(struct bpf_arena *arena, long uaddr)
>  }
>  
>  struct apply_range_data {
> +	struct bpf_arena *arena;
>  	struct page **pages;
> -	struct page *scratch_page;
>  	int i;
>  };
>  
>  struct clear_range_data {
> +	struct bpf_arena *arena;
>  	struct llist_head *free_pages;
> -	struct page *scratch_page;
>  };
>  
>  static int apply_range_set_cb(pte_t *pte, unsigned long addr, void *data)
> @@ -180,7 +180,7 @@ static int apply_range_set_cb(pte_t *pte, unsigned long addr, void *data)
>  
>  		if (pte_none(old))
>  			continue;
> -		if (WARN_ON_ONCE(pte_page(old) != d->scratch_page))
> +		if (WARN_ON_ONCE(pte_page(old) != d->arena->scratch_page))
>  			return -EBUSY;
>  		ptep_get_and_clear(&init_mm, addr, pte);
>  		flush_tlb_before_set(addr);
> @@ -227,7 +227,7 @@ static int apply_range_clear_cb(pte_t *pte, unsigned long addr, void *data)
>  	 * scratches its PTE. A later bpf_arena_free_pages() over that range walks
>  	 * here. Without the skip, scratch_page would be freed.
>  	 */
> -	if (page == d->scratch_page)
> +	if (page == d->arena->scratch_page)
>  		return 0;
>  
>  	__llist_add(&page->pcp_llist, d->free_pages);
> @@ -506,8 +506,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
>  	if (ret)
>  		goto out_sigsegv_memcg;
>  
> -	struct apply_range_data data = { .pages = &page, .i = 0,
> -					 .scratch_page = arena->scratch_page };
> +	struct apply_range_data data = { .arena = arena, .pages = &page, .i = 0 };
>  	/* Account into memcg of the process that created bpf_arena */
>  	ret = bpf_map_alloc_pages(map, NUMA_NO_NODE, 1, &page);
>  	if (ret) {
> @@ -696,8 +695,8 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
>  		bpf_map_memcg_exit(old_memcg, new_memcg);
>  		return 0;
>  	}
> +	data.arena = arena;
>  	data.pages = pages;
> -	data.scratch_page = arena->scratch_page;
>  
>  	if (raw_res_spin_lock_irqsave(&arena->spinlock, flags))
>  		goto out_free_pages;
> @@ -873,8 +872,8 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt,
>  	range_tree_set(&arena->rt, pgoff, page_cnt);
>  
>  	init_llist_head(&free_pages);
> +	cdata.arena = arena;
>  	cdata.free_pages = &free_pages;
> -	cdata.scratch_page = arena->scratch_page;
>  	/* clear ptes and collect struct pages */
>  	apply_to_existing_page_range(&init_mm, kaddr, page_cnt << PAGE_SHIFT,
>  				     apply_range_clear_cb, &cdata);
> @@ -981,8 +980,8 @@ static void arena_free_worker(struct work_struct *work)
>  	bpf_map_memcg_enter(&arena->map, &old_memcg, &new_memcg);
>  
>  	init_llist_head(&free_pages);
> +	cdata.arena = arena;
>  	cdata.free_pages = &free_pages;
> -	cdata.scratch_page = arena->scratch_page;
>  	arena_vm_start = bpf_arena_get_kern_vm_start(arena);
>  	user_vm_start = bpf_arena_get_user_vm_start(arena);
>