netdev - Re: [PATCH net-next 01/16] libeth: convert to netmem

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Message-ID: <20250527185749.5053f557@kernel.org>
Date: Tue, 27 May 2025 18:57:49 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Tony Nguyen <anthony.l.nguyen@...el.com>
Cc: davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.com,
 andrew+netdev@...n.ch, netdev@...r.kernel.org, Alexander Lobakin
 <aleksander.lobakin@...el.com>, maciej.fijalkowski@...el.com,
 magnus.karlsson@...el.com, michal.kubiak@...el.com,
 przemyslaw.kitszel@...el.com, ast@...nel.org, daniel@...earbox.net,
 hawk@...nel.org, john.fastabend@...il.com, horms@...nel.org,
 bpf@...r.kernel.org, Mina Almasry <almasrymina@...gle.com>
Subject: Re: [PATCH net-next 01/16] libeth: convert to netmem

On Tue, 20 May 2025 13:59:02 -0700 Tony Nguyen wrote:
> @@ -3277,16 +3277,20 @@ static u32 idpf_rx_hsplit_wa(const struct libeth_fqe *hdr,
>  			     struct libeth_fqe *buf, u32 data_len)
>  {
>  	u32 copy = data_len <= L1_CACHE_BYTES ? data_len : ETH_HLEN;
> +	struct page *hdr_page, *buf_page;
>  	const void *src;
>  	void *dst;
>  
> -	if (!libeth_rx_sync_for_cpu(buf, copy))
> +	if (unlikely(netmem_is_net_iov(buf->netmem)) ||
> +	    !libeth_rx_sync_for_cpu(buf, copy))
>  		return 0;

So what happens to the packet that landed in a netmem buffer in case
when HDS failed? I don't see the handling.

> -	dst = page_address(hdr->page) + hdr->offset + hdr->page->pp->p.offset;
> -	src = page_address(buf->page) + buf->offset + buf->page->pp->p.offset;
> -	memcpy(dst, src, LARGEST_ALIGN(copy));
> +	hdr_page = __netmem_to_page(hdr->netmem);
> +	buf_page = __netmem_to_page(buf->netmem);
> +	dst = page_address(hdr_page) + hdr->offset + hdr_page->pp->p.offset;
> +	src = page_address(buf_page) + buf->offset + buf_page->pp->p.offset;
>  
> +	memcpy(dst, src, LARGEST_ALIGN(copy));
>  	buf->offset += copy;
>  
>  	return copy;
> @@ -3302,11 +3306,12 @@ static u32 idpf_rx_hsplit_wa(const struct libeth_fqe *hdr,
>   */
>  struct sk_buff *idpf_rx_build_skb(const struct libeth_fqe *buf, u32 size)
>  {
> -	u32 hr = buf->page->pp->p.offset;
> +	struct page *buf_page = __netmem_to_page(buf->netmem);
> +	u32 hr = buf_page->pp->p.offset;
>  	struct sk_buff *skb;
>  	void *va;
>  
> -	va = page_address(buf->page) + buf->offset;
> +	va = page_address(buf_page) + buf->offset;
>  	prefetch(va + hr);

If you don't want to have to validate the low bit during netmem -> page
conversions - you need to clearly maintain the separation between 
the two in the driver. These __netmem_to_page() calls are too much of 
a liability.