From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 3705A31716A for ; Mon, 18 May 2026 09:33:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779096797; cv=none; b=nnpQUi+3VNjO9OQL+qTxPjmP+s1u9N59tcybppgYgidAHBEhyQKOlpm0e44uZeRjOb9zHTWt6uJttcI5MuIsNZMlyvx4uJCZ9oMPtT/WAfD9ENkKfMMihg6/PCWveHk9HTjGWwBgK3ToySdhUH3SeQtxNx44PSDrO9ElHdH3w7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779096797; c=relaxed/simple; bh=jSlre+l4xv2u3lht0ewJ63vmV7qP+xbiV5kD+x9/9jQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: In-Reply-To:Content-Type:Content-Disposition; b=ZiTPyQU7LVe5xpzVhQAKWzS72971eSkCpB1eVG3/OtupkVzZPm/Q/fjOLTCsEXGpjpzNh0XkTksSwzR4d7vI+v3d12pg+cfb9yXezmgpllMk6ikjRDGqa7YHU+jqVt7eoUWJA95zjRhyRIr0Tzc9uvNzxwEWnA+C9RrO7T5AafE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=H/CaEIFn; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="H/CaEIFn" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1779096795; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/rMc/AxTWnfe6rPr4aOrLy+F5Zu/TWf0k5shSHIhIko=; b=H/CaEIFnctrW8LwWROHQmclAXO14GVI//8RqNtIbFTUScJ1n4mAyViylj7JUvJX6A9aPlF mXAZ3LGiv9VgH0fV+DcElauqHi1xHRGb1XzKCxWxt1wrZLWmV0JI95J/REs7TOp2RSy5+3 d29Hw7uUUq8zJeOGdR/TExcKnJlVrcw= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-590-Q6Jo2tdIPp24hF7I6DVQlA-1; Mon, 18 May 2026 05:33:14 -0400 X-MC-Unique: Q6Jo2tdIPp24hF7I6DVQlA-1 X-Mimecast-MFC-AGG-ID: Q6Jo2tdIPp24hF7I6DVQlA_1779096793 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-45e80183514so426314f8f.3 for ; Mon, 18 May 2026 02:33:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779096793; x=1779701593; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=/rMc/AxTWnfe6rPr4aOrLy+F5Zu/TWf0k5shSHIhIko=; b=TZa7yhd474yZU5SbeFowfD+yPYUtJDRKEo8ROv8w679SUjyoW6D1p9mTc4lkEQeuXZ JJNTHnHDsf4P13PvsVYFLildBqkpfdb30Y7fD4ZVNZYpUzc/QgBllwPrUWlIIA9rh63E M4fwNnaFNFqZ52tRisoF57KiVn8JS/0QYGXfeqH9bXOfEtrLYWYn5XfKlLfz9PpIBC13 aQi24lBo4tAu7oKNsVvM7mZxGDSPfG1lR9IgPzBQ7rKzmVHnW7YOIXght8LdPU//eWjv Fy66XVUJYMKUnvWja9Ger8gFK1r9iYxog8e3lIFoFKvNnw+GiqHholhDA0ifcsnjtcL8 A8vg== X-Forwarded-Encrypted: i=1; AFNElJ9IwK9QRFEjpiNzO2+YsSFj4vkmMMKtgvxCTt+pf+CGdcgdc04K0/Ro9oAfb0RLXQ8pjyYpLZSy3Ny3uHHP/A==@lists.linux.dev X-Gm-Message-State: AOJu0YzdT8Lg2/oBz9Ibznh+x8yOJin8woD18TEXkkfX3ZVF5HSeqngo ArImI54oYRT3YWVwav3vPcYZLzA1KGp7mjbnwDYvckeNbLS/I3YBb8zgomKMHVnp6hAwh7GLhTx V99Ttgrw00ksQA7hQCrl8AlV3gd6G8zQnXh0Zn91p8Ln+OfqKxnMct76pwyqaqauqupk0 X-Gm-Gg: Acq92OFjM8uZTkMfgGBfbXLk3V9OPcywqS2xmxFo/MVFQrG5/dvH28fuR5IhAox75AI DdEj8Ox+5xJaZnGjtWB0zk5MdOqIvcUHASZei+M0SRLhVR3Vt0P/LERuHifQguCi25mCMzvuy9/ Wv3nekiHmbRJlLI0nr19B0BgQiZGhDu77TS1UqbnKRb2TLSwqNQfNzwBItBtNAf8MU09uFH1Q7c 0plorzZT5zl+sM/pikmihSW2zC8yhMIFSp5RAZPSNdPaYxGJkpnctUhpG09auldzESinVHfRd9R A0ErJMBxSxCd6clNTyzS98NY3waqKibUOFgXPrgV6QUXpdgrMe0lUxKDN1O+u/rdMJcpHN02hnZ tdTlQK0YfvIuIfAuxk46QJzVmby3oE65VWUK1QFDQ X-Received: by 2002:a05:600c:a406:b0:48f:e230:1d12 with SMTP id 5b1f17b1804b1-48fe6329913mr173599015e9.31.1779096792667; Mon, 18 May 2026 02:33:12 -0700 (PDT) X-Received: by 2002:a05:600c:a406:b0:48f:e230:1d12 with SMTP id 5b1f17b1804b1-48fe6329913mr173598345e9.31.1779096792146; Mon, 18 May 2026 02:33:12 -0700 (PDT) Received: from redhat.com (IGLD-80-230-48-7.inter.net.il. [80.230.48.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48febe5bc94sm140342335e9.4.2026.05.18.02.33.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 May 2026 02:33:11 -0700 (PDT) Date: Mon, 18 May 2026 05:33:08 -0400 From: "Michael S. Tsirkin" To: Stefano Garzarella Cc: David Laight , netdev@vger.kernel.org, Jakub Kicinski , Paolo Abeni , Simon Horman , Arseniy Krasnov , Stefan Hajnoczi , kvm@vger.kernel.org, Eric Dumazet , Eugenio =?iso-8859-1?Q?P=E9rez?= , Xuan Zhuo , virtualization@lists.linux.dev, "David S. Miller" , Jason Wang , linux-kernel@vger.kernel.org, Maher Azzouzi Subject: Re: [PATCH net] vsock/virtio: fix zerocopy completion for multi-skb sends Message-ID: <20260518053223-mutt-send-email-mst@kernel.org> References: <20260514092948.268720-1-sgarzare@redhat.com> <20260516125329.7b699c6f@pumpkin> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: mAcosM1BFljPJpwRdloRgO6wdVjRFloigOlSQeQsnaQ_1779096793 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, May 18, 2026 at 11:18:24AM +0200, Stefano Garzarella wrote: > On Sat, May 16, 2026 at 12:53:29PM +0100, David Laight wrote: > > On Thu, 14 May 2026 11:29:48 +0200 > > Stefano Garzarella wrote: > > > > > From: Stefano Garzarella > > > > > > When a large message is fragmented into multiple skbs, the zerocopy > > > uarg is only allocated and attached to the last skb in the loop. > > > Non-final skbs carry pinned user pages with no completion tracking, > > > so the kernel has no way to notify userspace when those pages are safe > > > to reuse. If the loop breaks early the uarg is never allocated at all, > > > leaking pinned pages with no completion notification. > > > > > > Fix this by following the approach used by TCP: allocate the zerocopy > > > uarg (if not provided by the caller) before the send loop and attach > > > it to every skb via skb_zcopy_set(), which takes a reference per skb. > > > Each skb's completion properly decrements the refcount, and the > > > notification only fires after the last skb is freed. > > > On failure, if no data was sent, the uarg is cleanly aborted via > > > net_zcopy_put_abort(). > > > > > > This issue was initially discovered by sashiko while reviewing commit > > > 1cb36e252211 ("vsock/virtio: fix MSG_ZEROCOPY pinned-pages accounting") > > > but was pre-existing. > > > > > > Fixes: 581512a6dc93 ("vsock/virtio: MSG_ZEROCOPY flag support") > > > Cc: Arseniy Krasnov > > > Closes: https://sashiko.dev/#/patchset/20260420132051.217589-1-sgarzare%40redhat.com > > > Reported-by: Maher Azzouzi > > > Signed-off-by: Stefano Garzarella > > > --- > > > net/vmw_vsock/virtio_transport_common.c | 83 ++++++++++--------------- > > > 1 file changed, 34 insertions(+), 49 deletions(-) > > > > > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > > > index 989cc252d3d3..1e3409d28164 100644 > > > --- a/net/vmw_vsock/virtio_transport_common.c > > > +++ b/net/vmw_vsock/virtio_transport_common.c > > > @@ -70,34 +70,6 @@ static bool virtio_transport_can_zcopy(const struct virtio_transport *t_ops, > > > return true; > > > } > > > > > > -static int virtio_transport_init_zcopy_skb(struct vsock_sock *vsk, > > > - struct sk_buff *skb, > > > - struct msghdr *msg, > > > - size_t pkt_len, > > > - bool zerocopy) > > > -{ > > > - struct ubuf_info *uarg; > > > - > > > - if (msg->msg_ubuf) { > > > - uarg = msg->msg_ubuf; > > > - net_zcopy_get(uarg); > > > - } else { > > > - struct ubuf_info_msgzc *uarg_zc; > > > - > > > - uarg = msg_zerocopy_realloc(sk_vsock(vsk), > > > - pkt_len, NULL, false); > > > - if (!uarg) > > > - return -1; > > > - > > > - uarg_zc = uarg_to_msgzc(uarg); > > > - uarg_zc->zerocopy = zerocopy ? 1 : 0; > > > - } > > > - > > > - skb_zcopy_init(skb, uarg); > > > - > > > - return 0; > > > -} > > > - > > > static int virtio_transport_fill_skb(struct sk_buff *skb, > > > struct virtio_vsock_pkt_info *info, > > > size_t len, > > > @@ -317,8 +289,10 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > > > u32 src_cid, src_port, dst_cid, dst_port; > > > const struct virtio_transport *t_ops; > > > struct virtio_vsock_sock *vvs; > > > + struct ubuf_info *uarg = NULL; > > > u32 pkt_len = info->pkt_len; > > > bool can_zcopy = false; > > > + bool have_uref = false; > > > u32 rest_len; > > > int ret; > > > > > > @@ -360,6 +334,25 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > > > if (can_zcopy) > > > max_skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, > > > (MAX_SKB_FRAGS * PAGE_SIZE)); > > > + > > > + if (info->msg->msg_flags & MSG_ZEROCOPY && > > > + info->op == VIRTIO_VSOCK_OP_RW) { > > > + uarg = info->msg->msg_ubuf; > > > + > > > + if (!uarg) { > > > + uarg = msg_zerocopy_realloc(sk_vsock(vsk), > > > + pkt_len, NULL, false); > > > + if (!uarg) { > > > + virtio_transport_put_credit(vvs, pkt_len); > > > + return -ENOMEM; > > > + } > > > + > > > + if (!can_zcopy) > > > + uarg_to_msgzc(uarg)->zerocopy = 0; > > > + > > > + have_uref = true; > > > + } > > > + } > > > > Surely that block should only be done if can_zcopy is true? > > And shouldn't something unset it if info->op != VIRTIO_VSOCK_OP_RW ? > > If the msg_zerocopy_realloc() fails then can't you just set can_zcopy to false. > > > > It info->msg->msg_buf is already set then I think you have to disable zero-copy. > > The caller has already requested a callback - and you can't add another. > > > > In any case by the end of this can_zcopy and have_uref are really the same flag. > > I kept the same approach we had before, trying to make as few changes as > possible. > > All these potential issues seem to be pre-existing and should be eventually > addressed in other patches IMHO. This patch one only resolves the main issue > of calling `skb_zcopy_set()` for every skb to avoid leaking pages, etc. the patch is upstream now, right? So pretty much have to be patches on top. > @Arseniy can you help on this? > > > > > > } > > > > > > rest_len = pkt_len; > > > @@ -378,27 +371,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > > > break; > > > } > > > > > > - /* We process buffer part by part, allocating skb on > > > - * each iteration. If this is last skb for this buffer > > > - * and MSG_ZEROCOPY mode is in use - we must allocate > > > - * completion for the current syscall. > > > - * > > > - * Pass pkt_len because msg iter is already consumed > > > - * by virtio_transport_fill_skb(), so iter->count > > > - * can not be used for RLIMIT_MEMLOCK pinned-pages > > > - * accounting done by msg_zerocopy_realloc(). > > > - */ > > > - if (info->msg && info->msg->msg_flags & MSG_ZEROCOPY && > > > - skb_len == rest_len && info->op == VIRTIO_VSOCK_OP_RW) { > > > - if (virtio_transport_init_zcopy_skb(vsk, skb, > > > - info->msg, > > > - pkt_len, > > > - can_zcopy)) { > > > - kfree_skb(skb); > > > - ret = -ENOMEM; > > > - break; > > > - } > > > - } > > > + skb_zcopy_set(skb, uarg, NULL); > > > > > > virtio_transport_inc_tx_pkt(vvs, skb); > > > > > > @@ -422,6 +395,18 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > > > > > > virtio_transport_put_credit(vvs, rest_len); > > > > > > + /* msg_zerocopy_realloc() initializes the ubuf_info refcnt to 1. > > > + * skb_zcopy_set() increases it for each skb, so we can drop that > > ^ must > > > > > + * initial reference to keep it balanced. > > > + */ > > > + if (have_uref) { > > > + if (rest_len == pkt_len) > > > + /* No data sent, abort the notification. */ > > > + net_zcopy_put_abort(uarg, true); > > > > Is it worth optimising for the 'nothing sent' case ? > > What do you suggest doing? > > I followed what TCP does. > > Thanks, > Stefano > > > > > -- David > > > > > + else > > > + net_zcopy_put(uarg); > > > + } > > > + > > > /* Return number of bytes, if any data has been sent. */ > > > if (rest_len != pkt_len) > > > ret = pkt_len - rest_len; > >