107 lines
3.5 KiB
Diff
107 lines
3.5 KiB
Diff
From 196ca1a79f81aae49e19aa6b0d7c940065aaf68f Mon Sep 17 00:00:00 2001
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From: Laurent Vivier <lvivier@redhat.com>
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Date: Wed, 7 Jan 2026 09:08:09 +0100
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Subject: [PATCH 19/20] udp_vu: Discard datagrams when RX virtqueue is not
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usable
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During vhost-user device initialization, UDP datagrams may arrive on
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listening sockets before the guest has enabled the RX virtqueue.
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When this happens, udp_vu_sock_recv() returns 0 without consuming
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the datagram from the socket. The caller, udp_sock_fwd(), uses a
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while loop with udp_peek_addr() to process pending datagrams. Since
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the datagram remains in the socket buffer, udp_peek_addr() keeps
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returning data available, causing a busy loop with 100% CPU usage.
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To avoid that, we need to discard the data when the virtqueue is not
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ready. udp_buf_sock_to_tap() actually does the same as it reads data
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with udp_sock_recv() and if fd_tap is not initialized tap_send_frames()
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drops them.
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Fixes: 28997fcb29b5 ("vhost-user: add vhost-user")
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Link: https://bugs.passt.top/show_bug.cgi?id=185
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Signed-off-by: Laurent Vivier <lvivier@redhat.com>
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Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
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Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
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(cherry picked from commit edac476e268e4a0c5759a32fea9c720056de6315)
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---
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udp_vu.c | 32 ++++++++++++++++++++++----------
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1 file changed, 22 insertions(+), 10 deletions(-)
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diff --git a/udp_vu.c b/udp_vu.c
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index c30dcf9..3774d53 100644
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--- a/udp_vu.c
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+++ b/udp_vu.c
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@@ -65,7 +65,8 @@ static size_t udp_vu_hdrlen(bool v6)
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* @v6: Set for IPv6 connections
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* @dlen: Size of received data (output)
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*
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- * Return: number of iov entries used to store the datagram
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+ * Return: number of iov entries used to store the datagram, 0 if the datagram
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+ * was discarded because the virtqueue is not ready, -1 on error
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*/
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static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
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bool v6, ssize_t *dlen)
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@@ -77,6 +78,15 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
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ASSERT(!c->no_udp);
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+ if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
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+ debug("Got UDP packet, but RX virtqueue not usable yet");
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+
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+ if (recvmsg(s, &msg, MSG_DONTWAIT) < 0)
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+ debug_perror("Failed to discard datagram");
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+
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+ return 0;
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+ }
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+
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/* compute L2 header length */
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hdrlen = udp_vu_hdrlen(v6);
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@@ -87,7 +97,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
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sizeof(struct virtio_net_hdr_mrg_rxbuf),
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NULL);
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if (iov_cnt == 0)
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- return 0;
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+ return -1;
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/* reserve space for the headers */
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ASSERT(iov_vu[0].iov_len >= MAX(hdrlen, ETH_ZLEN));
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@@ -101,7 +111,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
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*dlen = recvmsg(s, &msg, 0);
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if (*dlen < 0) {
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vu_queue_rewind(vq, iov_cnt);
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- return 0;
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+ return -1;
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}
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/* restore the pointer to the headers address */
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@@ -216,15 +226,17 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
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int iov_used;
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iov_used = udp_vu_sock_recv(c, vq, s, v6, &dlen);
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- if (iov_used <= 0)
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+ if (iov_used < 0)
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break;
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- udp_vu_prepare(c, toside, dlen);
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- if (*c->pcap) {
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- udp_vu_csum(toside, iov_used);
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- pcap_iov(iov_vu, iov_used,
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- sizeof(struct virtio_net_hdr_mrg_rxbuf));
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+ if (iov_used > 0) {
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+ udp_vu_prepare(c, toside, dlen);
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+ if (*c->pcap) {
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+ udp_vu_csum(toside, iov_used);
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+ pcap_iov(iov_vu, iov_used,
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+ sizeof(struct virtio_net_hdr_mrg_rxbuf));
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+ }
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+ vu_flush(vdev, vq, elem, iov_used);
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}
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- vu_flush(vdev, vq, elem, iov_used);
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}
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}
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--
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2.47.1
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