From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=ga9EtCKL; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTPS id 8B0915A026D for ; Mon, 09 Mar 2026 10:47:53 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1773049672; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=vHpf42VW01LL5nbeUfOkyIDO2STVzT5y5MUAwyej+k0=; b=ga9EtCKLQBqCcVIJ6Qn3qxVOnjwxZmi0J8y8QxiZTRMgt2tZwe+liVbTiytE2aObVpAK4b LndHfKu4mn49rjhJZTzRHoq9QT+W0LPgVPHXyeY6tAO3eP/MwCN3O/zre1Itq9+fWZbNlk EgYo4g4KZHEcMgstZhMi2SObGlx7N0M= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-583-yanKhVFSOBOs0Tb8FTNcaA-1; Mon, 09 Mar 2026 05:47:50 -0400 X-MC-Unique: yanKhVFSOBOs0Tb8FTNcaA-1 X-Mimecast-MFC-AGG-ID: yanKhVFSOBOs0Tb8FTNcaA_1773049669 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AD0FE1956060 for ; Mon, 9 Mar 2026 09:47:49 +0000 (UTC) Received: from lenovo-t14s.redhat.com (unknown [10.45.226.4]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B3CD41956095; Mon, 9 Mar 2026 09:47:48 +0000 (UTC) From: Laurent Vivier To: passt-dev@passt.top Subject: [PATCH v2 02/13] vhost-user: Centralise 802.3 frame padding in vu_collect() and vu_flush() Date: Mon, 9 Mar 2026 10:47:33 +0100 Message-ID: <20260309094744.1907754-3-lvivier@redhat.com> In-Reply-To: <20260309094744.1907754-1-lvivier@redhat.com> References: <20260309094744.1907754-1-lvivier@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Nv28giSgBKZGZiYovwNBObSOax_MIkNC837vcHDZoKw_1773049669 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Message-ID-Hash: ER35ZSW4CKC5FFFOAYX4N6R2SO7G3Y7Y X-Message-ID-Hash: ER35ZSW4CKC5FFFOAYX4N6R2SO7G3Y7Y X-MailFrom: lvivier@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Laurent Vivier X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: The per-protocol padding done by vu_pad() in tcp_vu.c and udp_vu.c was only correct for single-buffer frames, and assumed the padding area always fell within the first iov. It also relied on each caller computing the right MAX(..., ETH_ZLEN + VNET_HLEN) size for vu_collect() and calling vu_pad() at the right point. Centralise padding logic into the two shared vhost-user helpers instead: - vu_collect() now ensures at least ETH_ZLEN + VNET_HLEN bytes of buffer space are collected, so there is always room for a minimum-sized frame. - vu_flush() computes the actual frame length (accounting for VIRTIO_NET_F_MRG_RXBUF multi-buffer frames) and passes the padded length to vu_queue_fill(). A new iov_memset() helper in iov.c zero-fills the padding area in each buffer before iov_truncate() sets the logical frame size. The callers in tcp_vu.c, udp_vu.c and vu_send_single() use iov_memset() directly, replacing the now-removed vu_pad() helper and the MAX(..., ETH_ZLEN + VNET_HLEN) size calculations passed to vu_collect(). Centralising padding here will also ease the move to multi-iovec per element support, since there will be a single place to update. In vu_send_single(), fix padding, truncation and data copy to use the requested frame size rather than the total available buffer space from vu_collect(), which could be larger. Also add matching padding, truncation and explicit size to vu_collect() for the DUP_ACK path in tcp_vu_send_flag(). Signed-off-by: Laurent Vivier --- iov.c | 24 +++++++++++++++++++ iov.h | 2 ++ tcp_vu.c | 35 +++++++++++++++++---------- udp_vu.c | 12 ++++++---- vu_common.c | 69 +++++++++++++++++++++++++++++++---------------------- vu_common.h | 1 - 6 files changed, 96 insertions(+), 47 deletions(-) diff --git a/iov.c b/iov.c index 31a3f5bc29e5..cd48667226f3 100644 --- a/iov.c +++ b/iov.c @@ -169,6 +169,30 @@ size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size) return i; } +/** + * iov_memset() - Set bytes of an IO vector to a given value + * @iov: IO vector + * @iov_cnt: Number of elements in @iov + * @offset: Byte offset in the iovec at which to start + * @c: Byte value to fill with + * @length: Number of bytes to set + */ +void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c, + size_t length) +{ + size_t i; + + i = iov_skip_bytes(iov, iov_cnt, offset, &offset); + + for ( ; i < iov_cnt; i++) { + size_t n = MIN(iov[i].iov_len - offset, length); + + memset((char *)iov[i].iov_base + offset, c, n); + offset = 0; + length -= n; + } +} + /** * iov_tail_prune() - Remove any unneeded buffers from an IOV tail * @tail: IO vector tail (modified) diff --git a/iov.h b/iov.h index b4e50b0fca5a..d295d05b3bab 100644 --- a/iov.h +++ b/iov.h @@ -30,6 +30,8 @@ size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt, size_t offset, void *buf, size_t bytes); size_t iov_size(const struct iovec *iov, size_t iov_cnt); size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size); +void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c, + size_t length); /* * DOC: Theory of Operation, struct iov_tail diff --git a/tcp_vu.c b/tcp_vu.c index fd734e857b3b..3adead5f33fa 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -72,12 +72,12 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; struct vu_virtq_element flags_elem[2]; - size_t optlen, hdrlen, l2len; struct ipv6hdr *ip6h = NULL; struct iphdr *ip4h = NULL; struct iovec flags_iov[2]; struct tcp_syn_opts *opts; struct iov_tail payload; + size_t optlen, hdrlen; struct tcphdr *th; struct ethhdr *eh; uint32_t seq; @@ -90,7 +90,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) vu_set_element(&flags_elem[0], NULL, &flags_iov[0]); elem_cnt = vu_collect(vdev, vq, &flags_elem[0], 1, - MAX(hdrlen + sizeof(*opts), ETH_ZLEN + VNET_HLEN), NULL); + hdrlen + sizeof(*opts), NULL); if (elem_cnt != 1) return -1; @@ -131,6 +131,11 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) return ret; } + /* Pad short frames to ETH_ZLEN */ + if (ETH_ZLEN + VNET_HLEN > hdrlen + optlen) { + iov_memset(&flags_iov[0], 1, hdrlen + optlen, 0, + ETH_ZLEN + VNET_HLEN - (hdrlen + optlen)); + } iov_truncate(&flags_iov[0], 1, hdrlen + optlen); payload = IOV_TAIL(flags_elem[0].in_sg, 1, hdrlen); @@ -140,9 +145,6 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &payload, NULL, seq, !*c->pcap); - l2len = optlen + hdrlen - VNET_HLEN; - vu_pad(&flags_elem[0].in_sg[0], l2len); - if (*c->pcap) pcap_iov(&flags_elem[0].in_sg[0], 1, VNET_HLEN); nb_ack = 1; @@ -151,10 +153,17 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) vu_set_element(&flags_elem[1], NULL, &flags_iov[1]); elem_cnt = vu_collect(vdev, vq, &flags_elem[1], 1, - flags_elem[0].in_sg[0].iov_len, NULL); + hdrlen + optlen, NULL); if (elem_cnt == 1 && flags_elem[1].in_sg[0].iov_len >= flags_elem[0].in_sg[0].iov_len) { + /* Pad short frames to ETH_ZLEN */ + if (ETH_ZLEN + VNET_HLEN > hdrlen + optlen) { + iov_memset(&flags_iov[1], 1, hdrlen + optlen, 0, + ETH_ZLEN + VNET_HLEN - + (hdrlen + optlen)); + } + iov_truncate(&flags_iov[1], 1, hdrlen + optlen); memcpy(flags_elem[1].in_sg[0].iov_base, flags_elem[0].in_sg[0].iov_base, flags_elem[0].in_sg[0].iov_len); @@ -212,8 +221,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, cnt = vu_collect(vdev, vq, &elem[elem_cnt], VIRTQUEUE_MAX_SIZE - elem_cnt, - MAX(MIN(mss, fillsize) + hdrlen, ETH_ZLEN + VNET_HLEN), - &frame_size); + MIN(mss, fillsize) + hdrlen, &frame_size); if (cnt == 0) break; @@ -222,6 +230,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, /* reserve space for headers in iov */ iov = &elem[elem_cnt].in_sg[0]; ASSERT(iov->iov_len >= hdrlen); + iov->iov_base = (char *)iov->iov_base + hdrlen; iov->iov_len -= hdrlen; head[(*head_cnt)++] = elem_cnt; @@ -246,6 +255,11 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, if (!peek_offset_cap) ret -= already_sent; + /* Pad short frames to ETH_ZLEN */ + if (ETH_ZLEN + VNET_HLEN > (size_t)ret + hdrlen) { + iov_memset(&iov_vu[DISCARD_IOV_NUM], elem_cnt, ret, 0, + ETH_ZLEN + VNET_HLEN - (ret + hdrlen)); + } /* adjust iov number and length of the last iov */ i = iov_truncate(&iov_vu[DISCARD_IOV_NUM], elem_cnt, ret); @@ -443,7 +457,6 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) size_t frame_size = iov_size(iov, buf_cnt); bool push = i == head_cnt - 1; ssize_t dlen; - size_t l2len; ASSERT(frame_size >= hdrlen); @@ -457,10 +470,6 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) tcp_vu_prepare(c, conn, iov, buf_cnt, &check, !*c->pcap, push); - /* Pad first/single buffer only, it's at least ETH_ZLEN long */ - l2len = dlen + hdrlen - VNET_HLEN; - vu_pad(iov, l2len); - if (*c->pcap) pcap_iov(iov, buf_cnt, VNET_HLEN); diff --git a/udp_vu.c b/udp_vu.c index 5effca777e0a..ef9d26118eaf 100644 --- a/udp_vu.c +++ b/udp_vu.c @@ -73,7 +73,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, const struct vu_dev *vdev = c->vdev; struct msghdr msg = { 0 }; int iov_cnt, iov_used; - size_t hdrlen, l2len; + size_t hdrlen; ASSERT(!c->no_udp); @@ -98,6 +98,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, /* reserve space for the headers */ ASSERT(iov_vu[0].iov_len >= MAX(hdrlen, ETH_ZLEN + VNET_HLEN)); + iov_vu[0].iov_base = (char *)iov_vu[0].iov_base + hdrlen; iov_vu[0].iov_len -= hdrlen; @@ -115,12 +116,13 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, iov_vu[0].iov_base = (char *)iov_vu[0].iov_base - hdrlen; iov_vu[0].iov_len += hdrlen; + /* Pad short frames to ETH_ZLEN */ + if (ETH_ZLEN + VNET_HLEN > *dlen + hdrlen) { + iov_memset(iov_vu, iov_cnt, *dlen + hdrlen, 0, + ETH_ZLEN + VNET_HLEN - (*dlen + hdrlen)); + } iov_used = iov_truncate(iov_vu, iov_cnt, *dlen + hdrlen); - /* pad frame to 60 bytes: first buffer is at least ETH_ZLEN long */ - l2len = *dlen + hdrlen - VNET_HLEN; - vu_pad(&iov_vu[0], l2len); - vu_set_vnethdr(iov_vu[0].iov_base, iov_used); /* release unused buffers */ diff --git a/vu_common.c b/vu_common.c index 5f2ce18e5b71..8ea05dd30890 100644 --- a/vu_common.c +++ b/vu_common.c @@ -87,8 +87,8 @@ int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq, size_t current_size = 0; int elem_cnt = 0; + size = MAX(size, ETH_ZLEN + VNET_HLEN); /* 802.3 minimum size */ while (current_size < size && elem_cnt < max_elem) { - struct iovec *iov; int ret; ret = vu_queue_pop(vdev, vq, &elem[elem_cnt]); @@ -101,12 +101,12 @@ int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq, break; } - iov = &elem[elem_cnt].in_sg[0]; + elem[elem_cnt].in_num = iov_truncate(elem[elem_cnt].in_sg, + elem[elem_cnt].in_num, + size - current_size); - if (iov->iov_len > size - current_size) - iov->iov_len = size - current_size; - - current_size += iov->iov_len; + current_size += iov_size(elem[elem_cnt].in_sg, + elem[elem_cnt].in_num); elem_cnt++; if (!vu_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) @@ -143,10 +143,30 @@ void vu_set_vnethdr(struct virtio_net_hdr_mrg_rxbuf *vnethdr, int num_buffers) void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq, struct vu_virtq_element *elem, int elem_cnt) { - int i; - - for (i = 0; i < elem_cnt; i++) - vu_queue_fill(vdev, vq, &elem[i], elem[i].in_sg[0].iov_len, i); + int i, j, num_buffers; + + for (i = 0; i < elem_cnt; i += num_buffers) { + const struct virtio_net_hdr_mrg_rxbuf *vnethdr; + size_t len, padding, elem_size; + + vnethdr = elem[i].in_sg[0].iov_base; + num_buffers = le16toh(vnethdr->num_buffers); + + len = 0; + for (j = 0; j < num_buffers - 1; j++) { + elem_size = iov_size(elem[i + j].in_sg, + elem[i + j].in_num); + vu_queue_fill(vdev, vq, &elem[i + j], + elem_size, i + j); + len += elem_size; + } + /* pad the last element to have an 802.3 minimum frame size */ + elem_size = iov_size(elem[i + j].in_sg, elem[i + j].in_num); + padding = MAX(0, (ssize_t)(ETH_ZLEN + VNET_HLEN) - + (ssize_t)(len + elem_size)); + vu_queue_fill(vdev, vq, &elem[i + j], elem_size + padding, + i + j); + } vu_queue_flush(vdev, vq, elem_cnt); vu_queue_notify(vdev, vq); @@ -268,38 +288,31 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size) goto err; } + /* Pad short frames to ETH_ZLEN */ + if (size < ETH_ZLEN + VNET_HLEN) { + iov_memset(in_sg, elem_cnt, size, 0, + ETH_ZLEN + VNET_HLEN - size); + } + elem_cnt = iov_truncate(in_sg, elem_cnt, size); + vu_set_vnethdr(in_sg[0].iov_base, elem_cnt); - total -= VNET_HLEN; + size -= VNET_HLEN; /* copy data from the buffer to the iovec */ - iov_from_buf(in_sg, elem_cnt, VNET_HLEN, buf, total); + iov_from_buf(in_sg, elem_cnt, VNET_HLEN, buf, size); if (*c->pcap) pcap_iov(in_sg, elem_cnt, VNET_HLEN); vu_flush(vdev, vq, elem, elem_cnt); - trace("vhost-user sent %zu", total); + trace("vhost-user sent %zu", size); - return total; + return size; err: for (i = 0; i < elem_cnt; i++) vu_queue_detach_element(vq); return -1; } - -/** - * vu_pad() - Pad 802.3 frame to minimum length (60 bytes) if needed - * @iov: Buffer in iovec array where end of 802.3 frame is stored - * @l2len: Layer-2 length already filled in frame - */ -void vu_pad(struct iovec *iov, size_t l2len) -{ - if (l2len >= ETH_ZLEN) - return; - - memset((char *)iov->iov_base + iov->iov_len, 0, ETH_ZLEN - l2len); - iov->iov_len += ETH_ZLEN - l2len; -} diff --git a/vu_common.h b/vu_common.h index 865d9771fa89..5de0c987b936 100644 --- a/vu_common.h +++ b/vu_common.h @@ -61,6 +61,5 @@ void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq, void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref, const struct timespec *now); int vu_send_single(const struct ctx *c, const void *buf, size_t size); -void vu_pad(struct iovec *iov, size_t l2len); #endif /* VU_COMMON_H */ -- 2.53.0