netdev - Re: [PATCH net-next 03/16] libeth: xdp: add XDP

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Message-ID: <28b075ea-4126-4885-92a6-4633d4573f85@intel.com>
Date: Wed, 28 May 2025 16:57:15 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Tony Nguyen <anthony.l.nguyen@...el.com>, <davem@...emloft.net>,
	<pabeni@...hat.com>, <edumazet@...gle.com>, <andrew+netdev@...n.ch>,
	<netdev@...r.kernel.org>, <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>
Subject: Re: [PATCH net-next 03/16] libeth: xdp: add XDP_TX buffers sending

From: Jakub Kicinski <kuba@...nel.org>
Date: Tue, 27 May 2025 19:03:09 -0700

> On Tue, 20 May 2025 13:59:04 -0700 Tony Nguyen wrote:
>> +	if (sinfo || !netmem_is_net_iov(netmem)) {
>> +		const struct page_pool *pp = __netmem_get_pp(netmem);
>> +
>> +		dma_sync_single_for_device(pp->p.dev, desc.addr, desc.len,
>> +					   DMA_BIDIRECTIONAL);
>> +	}
> 
> How can we get an unreadable netmem into the XDP Tx path?

For now, it's not allowed. This is future proof. I have plans to allow
XDP and devmem to co-exist when the XDP program doesn't want to access
frags, only headers. In that case, why forbid?

Thanks,
Olek