From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E9C0C0032E for ; Tue, 7 Nov 2023 00:15:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233500AbjKGAPI (ORCPT ); Mon, 6 Nov 2023 19:15:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45948 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230248AbjKGAPG (ORCPT ); Mon, 6 Nov 2023 19:15:06 -0500 Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 372B1125 for ; Mon, 6 Nov 2023 16:14:58 -0800 (PST) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-5afa071d100so103189197b3.1 for ; Mon, 06 Nov 2023 16:14:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1699316097; x=1699920897; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=NJOStCOVHOX8afjyhZUr3wHzG9caGrOyErBNJl+fQsE=; b=WE79hAX87+nIxWPR1D1J0tdDpfokHaZko4+1kE0GZHSqYby78LJistdanP8UHFH/n5 OVVy0gLSVQu0dHTAUNrVF5H0Q0+0uanIljNl/Rt0WAyC4MOA+2OiHJWrRJxfOpcbKHfw cl2QwP+wG0qJ0phaK/aES5F3VOQKaySU8YxY546daZyIPBpNn8fC0FNGyABgV0pjp4DX ia+KfV7jds3McoDhe6qy3VyY6cW9VaQqPJ02QK2+SdP3BXL/vUNta1tTNG1g8mvBbiSX wsbrkN0v89rRFCXwHKDtLefwrEaDMKN8ViZ2JIvguPGFGQJNZg8vXhCOyTEAsKdoWn8t zhdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699316097; x=1699920897; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=NJOStCOVHOX8afjyhZUr3wHzG9caGrOyErBNJl+fQsE=; b=LKX7QqdZbmbiF3zip1oaKEejpBCcftIiVmmRpevUS1TVNLdkzA8CzcrA44HjH9Ox6N enIEV6nWNU0chFXF/3acXj0aOCt1+14yxooWGPwR0QqrU1W8kNC77JyPo1+m/gSx2K5B 5I4cqJze+Zf40fEU95XSEGRl35TVi8NCEgkzihDHSvZqQPasCaPK62veY/TCoh8WupZl 76rk/xWpRyawCrRZ4FVwuGV/rwQOVg4Kr9qerEv7zTd/GfBElTVCefFON/ITulwiEDXP lfitT+47rO+nSvCZWvkGjVRmBLLQPW/JE4b/3Cc6Vnsk6Ds7Ad818wgAtVoEUHWprUL+ T+dA== X-Gm-Message-State: AOJu0YxPrYQR/QdApg/I39cJy72It6ibWVJFZF8+7MvmN8W348h+sJgR eRepa4shdxPI9P3J82jnOjy6XTQ= X-Google-Smtp-Source: AGHT+IHee5oEAGC8m+DVisVJTqhCxMx4WoxETbeYezr61DtzdGwZMzI7W/00cgynnvTwgZdWg/F4Ggw= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a25:d785:0:b0:da0:5af7:d51a with SMTP id o127-20020a25d785000000b00da05af7d51amr642776ybg.0.1699316097113; Mon, 06 Nov 2023 16:14:57 -0800 (PST) Date: Mon, 6 Nov 2023 16:14:55 -0800 In-Reply-To: Mime-Version: 1.0 References: <20231106024413.2801438-10-almasrymina@google.com> <19129763-6f74-4b04-8a5f-441255b76d34@kernel.org> Message-ID: Subject: Re: [RFC PATCH v3 09/12] net: add support for skbs with unreadable frags From: Stanislav Fomichev To: Willem de Bruijn Cc: Mina Almasry , David Ahern , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Jesper Dangaard Brouer , Ilias Apalodimas , Arnd Bergmann , Shuah Khan , Sumit Semwal , "Christian =?utf-8?B?S8O2bmln?=" , Shakeel Butt , Jeroen de Borst , Praveen Kaligineedi , Willem de Bruijn , Kaiyuan Zhang Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/06, Willem de Bruijn wrote: > On Mon, Nov 6, 2023 at 3:55=E2=80=AFPM Stanislav Fomichev wrote: > > > > On Mon, Nov 6, 2023 at 3:27=E2=80=AFPM Mina Almasry wrote: > > > > > > On Mon, Nov 6, 2023 at 2:59=E2=80=AFPM Stanislav Fomichev wrote: > > > > > > > > On 11/06, Mina Almasry wrote: > > > > > On Mon, Nov 6, 2023 at 1:59=E2=80=AFPM Stanislav Fomichev wrote: > > > > > > > > > > > > On 11/06, Mina Almasry wrote: > > > > > > > On Mon, Nov 6, 2023 at 11:34=E2=80=AFAM David Ahern wrote: > > > > > > > > > > > > > > > > On 11/6/23 11:47 AM, Stanislav Fomichev wrote: > > > > > > > > > On 11/05, Mina Almasry wrote: > > > > > > > > >> For device memory TCP, we expect the skb headers to be a= vailable in host > > > > > > > > >> memory for access, and we expect the skb frags to be in = device memory > > > > > > > > >> and unaccessible to the host. We expect there to be no m= ixing and > > > > > > > > >> matching of device memory frags (unaccessible) with host= memory frags > > > > > > > > >> (accessible) in the same skb. > > > > > > > > >> > > > > > > > > >> Add a skb->devmem flag which indicates whether the frags= in this skb > > > > > > > > >> are device memory frags or not. > > > > > > > > >> > > > > > > > > >> __skb_fill_page_desc() now checks frags added to skbs fo= r page_pool_iovs, > > > > > > > > >> and marks the skb as skb->devmem accordingly. > > > > > > > > >> > > > > > > > > >> Add checks through the network stack to avoid accessing = the frags of > > > > > > > > >> devmem skbs and avoid coalescing devmem skbs with non de= vmem skbs. > > > > > > > > >> > > > > > > > > >> Signed-off-by: Willem de Bruijn > > > > > > > > >> Signed-off-by: Kaiyuan Zhang > > > > > > > > >> Signed-off-by: Mina Almasry > > > > > > > > >> > > > > > > > > >> --- > > > > > > > > >> include/linux/skbuff.h | 14 +++++++- > > > > > > > > >> include/net/tcp.h | 5 +-- > > > > > > > > >> net/core/datagram.c | 6 ++++ > > > > > > > > >> net/core/gro.c | 5 ++- > > > > > > > > >> net/core/skbuff.c | 77 +++++++++++++++++++++++++++= +++++++++------ > > > > > > > > >> net/ipv4/tcp.c | 6 ++++ > > > > > > > > >> net/ipv4/tcp_input.c | 13 +++++-- > > > > > > > > >> net/ipv4/tcp_output.c | 5 ++- > > > > > > > > >> net/packet/af_packet.c | 4 +-- > > > > > > > > >> 9 files changed, 115 insertions(+), 20 deletions(-) > > > > > > > > >> > > > > > > > > >> diff --git a/include/linux/skbuff.h b/include/linux/skbu= ff.h > > > > > > > > >> index 1fae276c1353..8fb468ff8115 100644 > > > > > > > > >> --- a/include/linux/skbuff.h > > > > > > > > >> +++ b/include/linux/skbuff.h > > > > > > > > >> @@ -805,6 +805,8 @@ typedef unsigned char *sk_buff_data_= t; > > > > > > > > >> * @csum_level: indicates the number of consecutive ch= ecksums found in > > > > > > > > >> * the packet minus one that have been verifie= d as > > > > > > > > >> * CHECKSUM_UNNECESSARY (max 3) > > > > > > > > >> + * @devmem: indicates that all the fragments in this s= kb are backed by > > > > > > > > >> + * device memory. > > > > > > > > >> * @dst_pending_confirm: need to confirm neighbour > > > > > > > > >> * @decrypted: Decrypted SKB > > > > > > > > >> * @slow_gro: state present at GRO time, slower prepar= e step required > > > > > > > > >> @@ -991,7 +993,7 @@ struct sk_buff { > > > > > > > > >> #if IS_ENABLED(CONFIG_IP_SCTP) > > > > > > > > >> __u8 csum_not_inet:1; > > > > > > > > >> #endif > > > > > > > > >> - > > > > > > > > >> + __u8 devmem:1; > > > > > > > > >> #if defined(CONFIG_NET_SCHED) || defined(CONFIG_NET_XGR= ESS) > > > > > > > > >> __u16 tc_index; /* traffic = control index */ > > > > > > > > >> #endif > > > > > > > > >> @@ -1766,6 +1768,12 @@ static inline void skb_zcopy_down= grade_managed(struct sk_buff *skb) > > > > > > > > >> __skb_zcopy_downgrade_managed(skb); > > > > > > > > >> } > > > > > > > > >> > > > > > > > > >> +/* Return true if frags in this skb are not readable by= the host. */ > > > > > > > > >> +static inline bool skb_frags_not_readable(const struct = sk_buff *skb) > > > > > > > > >> +{ > > > > > > > > >> + return skb->devmem; > > > > > > > > > > > > > > > > > > bikeshedding: should we also rename 'devmem' sk_buff flag= to 'not_readable'? > > > > > > > > > It better communicates the fact that the stack shouldn't = dereference the > > > > > > > > > frags (because it has 'devmem' fragments or for some othe= r potential > > > > > > > > > future reason). > > > > > > > > > > > > > > > > +1. > > > > > > > > > > > > > > > > Also, the flag on the skb is an optimization - a high level= signal that > > > > > > > > one or more frags is in unreadable memory. There is no requ= irement that > > > > > > > > all of the frags are in the same memory type. > > > > > > > > > > > > David: maybe there should be such a requirement (that they all = are > > > > > > unreadable)? Might be easier to support initially; we can relax= later > > > > > > on. > > > > > > > > > > > > > > > > Currently devmem =3D=3D not_readable, and the restriction is that= all the > > > > > frags in the same skb must be either all readable or all unreadab= le > > > > > (all devmem or all non-devmem). > > > > > > > > > > > > The flag indicates that the skb contains all devmem dma-buf m= emory > > > > > > > specifically, not generic 'not_readable' frags as the comment= says: > > > > > > > > > > > > > > + * @devmem: indicates that all the fragments in this skb= are backed by > > > > > > > + * device memory. > > > > > > > > > > > > > > The reason it's not a generic 'not_readable' flag is because = handing > > > > > > > off a generic not_readable skb to the userspace is semantical= ly not > > > > > > > what we're doing. recvmsg() is augmented in this patch series= to > > > > > > > return a devmem skb to the user via a cmsg_devmem struct whic= h refers > > > > > > > specifically to the memory in the dma-buf. recvmsg() in this = patch > > > > > > > series is not augmented to give any 'not_readable' skb to the > > > > > > > userspace. > > > > > > > > > > > > > > IMHO skb->devmem + an skb_frags_not_readable() as implemented= is > > > > > > > correct. If a new type of unreadable skbs are introduced to t= he stack, > > > > > > > I imagine the stack would implement: > > > > > > > > > > > > > > 1. new header flag: skb->newmem > > > > > > > 2. > > > > > > > > > > > > > > static inline bool skb_frags_not_readable(const struct skb_bu= ff *skb) > > > > > > > { > > > > > > > return skb->devmem || skb->newmem; > > > > > > > } > > > > > > > > > > > > > > 3. tcp_recvmsg_devmem() would handle skb->devmem skbs is in t= his patch > > > > > > > series, but tcp_recvmsg_newmem() would handle skb->newmem skb= s. > > > > > > > > > > > > You copy it to the userspace in a special way because your frag= s > > > > > > are page_is_page_pool_iov(). I agree with David, the skb bit is > > > > > > just and optimization. > > > > > > > > > > > > For most of the core stack, it doesn't matter why your skb is n= ot > > > > > > readable. For a few places where it matters (recvmsg?), you can > > > > > > double-check your frags (all or some) with page_is_page_pool_io= v. > > > > > > > > > > > > > > > > I see, we can do that then. I.e. make the header flag 'not_readab= le' > > > > > and check the frags to decide to delegate to tcp_recvmsg_devmem()= or > > > > > something else. We can even assume not_readable =3D=3D devmem bec= ause > > > > > currently devmem is the only type of unreadable frag currently. > > > > > > > > > > > Unrelated: we probably need socket to dmabuf association as wel= l (via > > > > > > netlink or something). > > > > > > > > > > Not sure this is possible. The dma-buf is bound to the rx-queue, = and > > > > > any packets that land on that rx-queue are bound to that dma-buf, > > > > > regardless of which socket that packet belongs to. So the associa= tion > > > > > IMO must be rx-queue to dma-buf, not socket to dma-buf. > > > > > > > > But there is still always 1 dmabuf to 1 socket association (on rx),= right? > > > > Because otherwise, there is no way currently to tell, at recvmsg, w= hich > > > > dmabuf the received token belongs to. > > > > > > > > > > Yes, but this 1 dma-buf to 1 socket association happens because the > > > user binds the dma-buf to an rx-queue and configures flow steering of > > > the socket to that rx-queue. > > > > It's still fixed and won't change during the socket lifetime, right? > > And the socket has to know this association; otherwise those tokens > > are useless since they don't carry anything to identify the dmabuf. > > > > I think my other issue with MSG_SOCK_DEVMEM being on recvmsg is that > > it somehow implies that I have an option of passing or not passing it > > for an individual system call. > > If we know that we're going to use dmabuf with the socket, maybe we > > should move this flag to the socket() syscall? > > > > fd =3D socket(AF_INET6, SOCK_STREAM, SOCK_DEVMEM); > > > > ? >=20 > I think it should then be a setsockopt called before any data is > exchanged, with no change of modifying mode later. We generally use > setsockopts for the mode of a socket. This use of the protocol field > in socket() for setting a mode would be novel. Also, it might miss > passively opened connections, or be overly restrictive: one approach > for all accepted child sockets. I was thinking this is similar to SOCK_CLOEXEC or SOCK_NONBLOCK? There are plenty of bits we can grab. But setsockopt works as well!