netdev - Re: [PATCH bpf-next v2 1/2] xsk: store struct xdp_sock as a flexible array member of the XSKMAP

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Date:   Mon, 28 Oct 2019 10:55:08 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, magnus.karlsson@...il.com,
        magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
        toke@...hat.com
Subject: Re: [PATCH bpf-next v2 1/2] xsk: store struct xdp_sock as a
 flexible array member of the XSKMAP

On Fri, 25 Oct 2019 09:18:40 +0200, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
> 
> Prior this commit, the array storing XDP socket instances were stored
> in a separate allocated array of the XSKMAP. Now, we store the sockets
> as a flexible array member in a similar fashion as the arraymap. Doing
> so, we do less pointer chasing in the lookup.
> 
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>

Thanks for the re-spin.

> diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c
> index 82a1ffe15dfa..a83e92fe2971 100644
> --- a/kernel/bpf/xskmap.c
> +++ b/kernel/bpf/xskmap.c

> @@ -92,44 +93,35 @@ static struct bpf_map *xsk_map_alloc(union bpf_attr *attr)
>  	    attr->map_flags & ~(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY))
>  		return ERR_PTR(-EINVAL);
>  
> -	m = kzalloc(sizeof(*m), GFP_USER);
> -	if (!m)
> +	numa_node = bpf_map_attr_numa_node(attr);
> +	size = struct_size(m, xsk_map, attr->max_entries);
> +	cost = size + array_size(sizeof(*m->flush_list), num_possible_cpus());

Now we didn't use array_size() previously because the sum here may
overflow.

We could use __ab_c_size() here, the name is probably too ugly to use
directly and IDK what we'd have to name such a accumulation helper...

So maybe just make cost and size a u64 and we should be in the clear.

> +	err = bpf_map_charge_init(&mem, cost);
> +	if (err < 0)
> +		return ERR_PTR(err);
> +
> +	m = bpf_map_area_alloc(size, numa_node);
> +	if (!m) {
> +		bpf_map_charge_finish(&mem);
>  		return ERR_PTR(-ENOMEM);
> +	}
>  
>  	bpf_map_init_from_attr(&m->map, attr);
> +	bpf_map_charge_move(&m->map.memory, &mem);
>  	spin_lock_init(&m->lock);
>  
> -	cost = (u64)m->map.max_entries * sizeof(struct xdp_sock *);
> -	cost += sizeof(struct list_head) * num_possible_cpus();
> -
> -	/* Notice returns -EPERM on if map size is larger than memlock limit */
> -	err = bpf_map_charge_init(&m->map.memory, cost);
> -	if (err)
> -		goto free_m;
> -
> -	err = -ENOMEM;
> -
>  	m->flush_list = alloc_percpu(struct list_head);
> -	if (!m->flush_list)
> -		goto free_charge;
> +	if (!m->flush_list) {
> +		bpf_map_charge_finish(&m->map.memory);
> +		bpf_map_area_free(m);
> +		return ERR_PTR(-ENOMEM);
> +	}
>  
>  	for_each_possible_cpu(cpu)
>  		INIT_LIST_HEAD(per_cpu_ptr(m->flush_list, cpu));
>  
> -	m->xsk_map = bpf_map_area_alloc(m->map.max_entries *
> -					sizeof(struct xdp_sock *),
> -					m->map.numa_node);
> -	if (!m->xsk_map)
> -		goto free_percpu;
>  	return &m->map;
> -
> -free_percpu:
> -	free_percpu(m->flush_list);
> -free_charge:
> -	bpf_map_charge_finish(&m->map.memory);
> -free_m:
> -	kfree(m);
> -	return ERR_PTR(err);
>  }
>  
>  static void xsk_map_free(struct bpf_map *map)