netdev - Re: [PATCH v4 bpf-next 09/13] bpf: introduce multibuff support to bpf_prog_test_run

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Date:   Thu, 8 Oct 2020 11:06:14 +0300
From:   Shay Agroskin <shayagr@...zon.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <davem@...emloft.net>, <kuba@...nel.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, <sameehj@...zon.com>,
        <john.fastabend@...il.com>, <dsahern@...nel.org>,
        <brouer@...hat.com>, <lorenzo.bianconi@...hat.com>,
        <echaudro@...hat.com>
Subject: Re: [PATCH v4 bpf-next 09/13] bpf: introduce multibuff support to
 bpf_prog_test_run_xdp()


Lorenzo Bianconi <lorenzo@...nel.org> writes:

> Introduce the capability to allocate a xdp multi-buff in
> bpf_prog_test_run_xdp routine. This is a preliminary patch to 
> introduce
> the selftests for new xdp multi-buff ebpf helpers
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  net/bpf/test_run.c | 51 
>  ++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 43 insertions(+), 8 deletions(-)
>
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index bd291f5f539c..ec7286cd051b 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -617,44 +617,79 @@ int bpf_prog_test_run_xdp(struct bpf_prog 
> *prog, const union bpf_attr *kattr,
>  {
>  	u32 tailroom = SKB_DATA_ALIGN(sizeof(struct 
>  skb_shared_info));
>  	u32 headroom = XDP_PACKET_HEADROOM;
> -	u32 size = kattr->test.data_size_in;
>  	u32 repeat = kattr->test.repeat;
>  	struct netdev_rx_queue *rxqueue;
> +	struct skb_shared_info *sinfo;
>  	struct xdp_buff xdp = {};
> +	u32 max_data_sz, size;
>  	u32 retval, duration;
> -	u32 max_data_sz;
> +	int i, ret, data_len;
>  	void *data;
> -	int ret;
>  
>  	if (kattr->test.ctx_in || kattr->test.ctx_out)
>  		return -EINVAL;
>  
> -	/* XDP have extra tailroom as (most) drivers use full page 
> */
>  	max_data_sz = 4096 - headroom - tailroom;

For the sake of consistency, can this 4096 be changed to PAGE_SIZE 
?
Same as in
     data_len = min_t(int, kattr->test.data_size_in - size, 
     PAGE_SIZE);

expression below

> +	size = min_t(u32, kattr->test.data_size_in, max_data_sz);
> +	data_len = size;
>  
> -	data = bpf_test_init(kattr, kattr->test.data_size_in,
> -			     max_data_sz, headroom, tailroom);
> +	data = bpf_test_init(kattr, size, max_data_sz, headroom, 
> tailroom);
>  	if (IS_ERR(data))
>  		return PTR_ERR(data);
>  
>  	xdp.data_hard_start = data;
>  	xdp.data = data + headroom;
>  	xdp.data_meta = xdp.data;
> -	xdp.data_end = xdp.data + size;
> +	xdp.data_end = xdp.data + data_len;
>  	xdp.frame_sz = headroom + max_data_sz + tailroom;
>  
> +	sinfo = xdp_get_shared_info_from_buff(&xdp);
> +	if (unlikely(kattr->test.data_size_in > size)) {
> +		void __user *data_in = 
> u64_to_user_ptr(kattr->test.data_in);
> +
> +		while (size < kattr->test.data_size_in) {
> +			skb_frag_t *frag = 
> &sinfo->frags[sinfo->nr_frags];
> +			struct page *page;
> +			int data_len;
> +
> +			page = alloc_page(GFP_KERNEL);
> +			if (!page) {
> +				ret = -ENOMEM;
> +				goto out;
> +			}
> +
> +			__skb_frag_set_page(frag, page);
> +			data_len = min_t(int, 
> kattr->test.data_size_in - size,
> +					 PAGE_SIZE);
> +			skb_frag_size_set(frag, data_len);
> +			if (copy_from_user(page_address(page), 
> data_in + size,
> +					   data_len)) {
> +				ret = -EFAULT;
> +				goto out;
> +			}
> +			sinfo->nr_frags++;
> +			size += data_len;
> +		}
> +		xdp.mb = 1;
> +	}
> +
>  	rxqueue = 
>  __netif_get_rx_queue(current->nsproxy->net_ns->loopback_dev, 
>  0);
>  	xdp.rxq = &rxqueue->xdp_rxq;
>  	bpf_prog_change_xdp(NULL, prog);
>  	ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration, 
>  true);
>  	if (ret)
>  		goto out;
> +
>  	if (xdp.data != data + headroom || xdp.data_end != 
>  xdp.data + size)
> -		size = xdp.data_end - xdp.data;
> +		size += xdp.data_end - xdp.data - data_len;

Can we please drop the variable shadowing of data_len ? This is 
confusing since the initial value of data_len is correct in the 
`size` calculation, while its value inside the while loop it not.

This seem to be syntactically correct, but I think it's better 
practice to avoid shadowing here.

> +
>  	ret = bpf_test_finish(kattr, uattr, xdp.data, size, 
>  retval, duration);
>  out:
>  	bpf_prog_change_xdp(prog, NULL);
> +	for (i = 0; i < sinfo->nr_frags; i++)
> +		__free_page(skb_frag_page(&sinfo->frags[i]));
>  	kfree(data);
> +
>  	return ret;
>  }