From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE346FBE1
	for <netdev@vger.kernel.org>; Mon,  3 Jul 2023 14:45:40 +0000 (UTC)
Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09284C433C7;
	Mon,  3 Jul 2023 14:45:38 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
	s=k20201202; t=1688395540;
	bh=D01JRZ6YxzSYbxJrhvbB7jt0pV/WAPNqrzz0yrSDBY4=;
	h=Date:Subject:To:Cc:References:From:In-Reply-To:From;
	b=nid7zAbx5g66G0jxhPwIuRrSe6clrHM+diWwYK36r5HLou+d21CdoXV1kKd99ae/k
	 plsXDrsHdZPBWAb505ac6PTNUSyXrill8bz0q5G+5qeEfdCw0pjQhF7gNOgaQQHQmq
	 RlLHGRGE7Oiy0wHSzLOPlIBjthQiVu3ej+HM05RRuoZ/ajSb5XDRfiEaDU40VbB4x/
	 R64zJ4uiFke89Lf2kCIDMclGvXOekCa2yqceZlcS0XIKZocuOQXafgltwj7hJzwFmf
	 JY1acKGcAF68LxFF1ydiGLW4Mf4ujSSY+ctIwaxY1AP3pgtrMbCbwaDLAoF5ssPPs8
	 Zv/3fbrJMvFnw==
Message-ID: <47b79e77-461b-8fe9-41fb-b69a6b205ef2@kernel.org>
Date: Mon, 3 Jul 2023 08:45:38 -0600
Precedence: bulk
X-Mailing-List: netdev@vger.kernel.org
List-Id: <netdev.vger.kernel.org>
List-Subscribe: <mailto:netdev+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:netdev+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0)
 Gecko/20100101 Thunderbird/102.12.0
Subject: Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5]
 page_pool: remove PP_FLAG_PAGE_FRAG flag)
Content-Language: en-US
To: Mina Almasry <almasrymina@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
 Jesper Dangaard Brouer <jbrouer@redhat.com>, brouer@redhat.com,
 Alexander Duyck <alexander.duyck@gmail.com>,
 Yunsheng Lin <linyunsheng@huawei.com>, davem@davemloft.net,
 pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
 Lorenzo Bianconi <lorenzo@kernel.org>, Yisen Zhuang
 <yisen.zhuang@huawei.com>, Salil Mehta <salil.mehta@huawei.com>,
 Eric Dumazet <edumazet@google.com>, Sunil Goutham <sgoutham@marvell.com>,
 Geetha sowjanya <gakula@marvell.com>, Subbaraya Sundeep
 <sbhatta@marvell.com>, hariprasad <hkelam@marvell.com>,
 Saeed Mahameed <saeedm@nvidia.com>, Leon Romanovsky <leon@kernel.org>,
 Felix Fietkau <nbd@nbd.name>, Ryder Lee <ryder.lee@mediatek.com>,
 Shayne Chen <shayne.chen@mediatek.com>, Sean Wang <sean.wang@mediatek.com>,
 Kalle Valo <kvalo@kernel.org>, Matthias Brugger <matthias.bgg@gmail.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>,
 Jesper Dangaard Brouer <hawk@kernel.org>,
 Ilias Apalodimas <ilias.apalodimas@linaro.org>, linux-rdma@vger.kernel.org,
 linux-wireless@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
 linux-mediatek@lists.infradead.org, Jonathan Lemon <jonathan.lemon@gmail.com>
References: <20230612130256.4572-1-linyunsheng@huawei.com>
 <20230612130256.4572-5-linyunsheng@huawei.com>
 <20230614101954.30112d6e@kernel.org>
 <8c544cd9-00a3-2f17-bd04-13ca99136750@huawei.com>
 <20230615095100.35c5eb10@kernel.org>
 <CAKgT0Uc6Xoyh3Edgt+83b+HTM5j4JDr3fuxcyL9qDk+Wwt9APg@mail.gmail.com>
 <908b8b17-f942-f909-61e6-276df52a5ad5@huawei.com>
 <CAKgT0UeZfbxDYaeUntrQpxHmwCh6zy0dEpjxghiCNxPxv=kdoQ@mail.gmail.com>
 <72ccf224-7b45-76c5-5ca9-83e25112c9c6@redhat.com>
 <20230616122140.6e889357@kernel.org>
 <eadebd58-d79a-30b6-87aa-1c77acb2ec17@redhat.com>
 <20230619110705.106ec599@kernel.org>
 <CAHS8izOySGEcXmMg3Gbb5DS-D9-B165gNpwf5a+ObJ7WigLmHg@mail.gmail.com>
 <5e0ac5bb-2cfa-3b58-9503-1e161f3c9bd5@kernel.org>
 <CAHS8izP2fPS56uXKMCnbKnPNn=xhTd0SZ1NRUgnAvyuSeSSjGA@mail.gmail.com>
From: David Ahern <dsahern@kernel.org>
In-Reply-To: <CAHS8izP2fPS56uXKMCnbKnPNn=xhTd0SZ1NRUgnAvyuSeSSjGA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

On 7/3/23 12:22 AM, Mina Almasry wrote:
> tcpdump is able to access the header of these skbs which is in host
> memory, but not the payload in device memory. Here is an example
> session with my netcat-like test for device memory TCP:
> https://pastebin.com/raw/FRjKf0kv
> 
> tcpdump seems to work, and the length of the packets above is correct.
> tcpdump -A however isn't able to print the payload of the packets:
> https://pastebin.com/raw/2PcNxaZV

That is my expectation. The tcpdump is just an easy example of accessing
the skb page frags. skb_copy_and_csum_bits used by icmp is another
example that can walk frags wanting access to device memory. You did not
cause a panic or trip a WARN_ON for example with the tcpdump?

Thanks for checking.