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GET /api/patches/2194226/?format=api
{ "id": 2194226, "url": "http://patchwork.ozlabs.org/api/patches/2194226/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260207134728.1495932-8-lulu@redhat.com/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260207134728.1495932-8-lulu@redhat.com>", "list_archive_url": null, "date": "2026-02-07T13:47:24", "name": "[08/12] virtio-net: disable backend poll while stopped by default", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "0d5b830a5e11717d57ca83ef83cccc172522da05", "submitter": { "id": 78960, "url": "http://patchwork.ozlabs.org/api/people/78960/?format=api", "name": "Cindy Lu", "email": "lulu@redhat.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260207134728.1495932-8-lulu@redhat.com/mbox/", "series": [ { "id": 491379, "url": "http://patchwork.ozlabs.org/api/series/491379/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=491379", "date": "2026-02-07T13:47:17", "name": "[01/12] net: introduce read_poll/write_poll", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/491379/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2194226/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2194226/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=dTy3IDNv;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)" ], "Received": [ "from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4f7XPr1YF1z1xvj\n\tfor <incoming@patchwork.ozlabs.org>; Sun, 08 Feb 2026 00:49:36 +1100 (AEDT)", "from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from <qemu-devel-bounces@nongnu.org>)\n\tid 1voigU-0003eL-Au; Sat, 07 Feb 2026 08:49:21 -0500", "from eggs.gnu.org ([2001:470:142:3::10])\n by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <lulu@redhat.com>) id 1voifx-0003Lq-On\n for qemu-devel@nongnu.org; Sat, 07 Feb 2026 08:48:43 -0500", "from us-smtp-delivery-124.mimecast.com ([170.10.133.124])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <lulu@redhat.com>) id 1voifv-0003Fp-IJ\n for qemu-devel@nongnu.org; Sat, 07 Feb 2026 08:48:41 -0500", "from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com\n (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by\n relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3,\n cipher=TLS_AES_256_GCM_SHA384) id us-mta-280-_OKPVU8wOQWjQxXQBNJH_A-1; Sat,\n 07 Feb 2026 08:48:37 -0500", "from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com\n (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest\n SHA256)\n (No client certificate requested)\n by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS\n id 9613118003FC; Sat, 7 Feb 2026 13:48:36 +0000 (UTC)", "from S2.redhat.com (unknown [10.72.112.15])\n by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP\n id 72CF230001A8; Sat, 7 Feb 2026 13:48:32 +0000 (UTC)" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1770472118;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:mime-version:mime-version:\n content-transfer-encoding:content-transfer-encoding:\n in-reply-to:in-reply-to:references:references;\n bh=sLH/nCdIPlCaFM08m7QBinpS9H2mQdsoowpj1lshi04=;\n b=dTy3IDNvZlR0BCDGpOpFUAHwcDpeibOrGZEAoSCgsVfkGToLjlhhaM9vb9VCaUg8LbqCNy\n 3Nbx31D6WE3l2yxdLERJZoekygKnjKqWFu6DUKqC23Yp+DXZK9hJnaSsTENSsCnbNL25z4\n ftoOns7gzZ1qKtb/DRxZJS2pKsy4wtI=", "X-MC-Unique": "_OKPVU8wOQWjQxXQBNJH_A-1", "X-Mimecast-MFC-AGG-ID": "_OKPVU8wOQWjQxXQBNJH_A_1770472116", "From": "Cindy Lu <lulu@redhat.com>", "To": "lulu@redhat.com, mst@redhat.com, jasowang@redhat.com, zhangckid@gmail.com,\n lizhijian@fujitsu.com, qemu-devel@nongnu.org", "Subject": "[PATCH 08/12] virtio-net: disable backend poll while stopped by\n default", "Date": "Sat, 7 Feb 2026 21:47:24 +0800", "Message-ID": "<20260207134728.1495932-8-lulu@redhat.com>", "In-Reply-To": "<20260207134728.1495932-1-lulu@redhat.com>", "References": "<20260207134728.1495932-1-lulu@redhat.com>", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-Scanned-By": "MIMEDefang 3.4.1 on 10.30.177.4", "Received-SPF": "pass client-ip=170.10.133.124; envelope-from=lulu@redhat.com;\n helo=us-smtp-delivery-124.mimecast.com", "X-Spam_score_int": "-20", "X-Spam_score": "-2.1", "X-Spam_bar": "--", "X-Spam_report": "(-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001,\n RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001,\n SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no", "X-Spam_action": "no action", "X-BeenThere": "qemu-devel@nongnu.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "qemu development <qemu-devel.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-devel>", "List-Post": "<mailto:qemu-devel@nongnu.org>", "List-Help": "<mailto:qemu-devel-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "From: Jason Wang <jasowang@redhat.com>\n\nWhen the VM is stopped, reading from the backend (e.g. tap) can pull host\ntraffic into QEMU queues at a point where the core networking code may flush\nor purge queued packets on vmstop to avoid state changes while not running.\nThis can show up as intermittent packet loss around stop/resume transitions.\n\nRegister a virtio-net vm change state handler that disables backend read_poll()\nwhile the VM is stopped, and re-enables it when the VM runs again. Use a\nhigher priority so it runs early on vmstop, while allowing netfilter pipelines\n(e.g. redirector with enable_when_stopped) to re-enable polling explicitly\nwhen they are ready to handle traffic.\n\nSigned-off-by: Jason Wang <jasowang@redhat.com>\nSigned-off-by: Cindy Lu <lulu@redhat.com>\n---\n hw/net/virtio-net.c | 47 ++++++++++++++++++++++++++++++++++\n include/hw/virtio/virtio-net.h | 2 ++\n 2 files changed, 49 insertions(+)", "diff": "diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c\nindex 17ed0ef919..d6d2188863 100644\n--- a/hw/net/virtio-net.c\n+++ b/hw/net/virtio-net.c\n@@ -41,6 +41,7 @@\n #include \"standard-headers/linux/ethtool.h\"\n #include \"system/system.h\"\n #include \"system/replay.h\"\n+#include \"system/runstate.h\"\n #include \"trace.h\"\n #include \"monitor/qdev.h\"\n #include \"monitor/monitor.h\"\n@@ -1310,6 +1311,38 @@ static void virtio_net_disable_rss(VirtIONet *n)\n virtio_net_commit_rss_config(n);\n }\n \n+static void virtio_net_backend_read_poll_set(VirtIONet *n, bool enable)\n+{\n+ int i;\n+\n+ if (!n->nic) {\n+ return;\n+ }\n+\n+ for (i = 0; i < (int)n->max_ncs; i++) {\n+ NetClientState *frontend = qemu_get_subqueue(n->nic, i);\n+ NetClientState *backend = frontend ? frontend->peer : NULL;\n+\n+ if (backend && backend->info && backend->info->read_poll) {\n+ backend->info->read_poll(backend, enable);\n+ }\n+ }\n+}\n+\n+static void virtio_net_vm_state_change_backend_poll(void *opaque, bool running,\n+ RunState state)\n+{\n+ VirtIONet *n = opaque;\n+\n+ /*\n+ * Prevent backend (e.g. tap) from reading packets while the VM is stopped.\n+ * This avoids pulling host->guest traffic into QEMU queues that may be\n+ * purged on vmstop, and lets netfilter pipelines (e.g. redirector+buffer)\n+ * explicitly re-enable polling when they are ready.\n+ */\n+ virtio_net_backend_read_poll_set(n, running);\n+}\n+\n static bool virtio_net_load_ebpf_fds(VirtIONet *n, Error **errp)\n {\n int fds[EBPF_RSS_MAX_FDS] = { [0 ... EBPF_RSS_MAX_FDS - 1] = -1};\n@@ -4047,6 +4080,15 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)\n n->rss_data.specified_hash_types.on_bits |\n n->rss_data.specified_hash_types.auto_bits;\n }\n+\n+ /*\n+ * Default behavior: use a higher priority than netfilter redirector\n+ * handlers (default 0) so that on vmstop we disable first, and redirectors\n+ * can re-enable read_poll after this if enable_when_stopped is set.\n+ */\n+ n->backend_poll_vmstate =\n+ qemu_add_vm_change_state_handler_prio(\n+ virtio_net_vm_state_change_backend_poll, n, 10);\n }\n \n static void virtio_net_device_unrealize(DeviceState *dev)\n@@ -4059,6 +4101,11 @@ static void virtio_net_device_unrealize(DeviceState *dev)\n virtio_net_unload_ebpf(n);\n }\n \n+ if (n->backend_poll_vmstate) {\n+ qemu_del_vm_change_state_handler(n->backend_poll_vmstate);\n+ n->backend_poll_vmstate = NULL;\n+ }\n+\n /* This will stop vhost backend if appropriate. */\n virtio_net_set_status(vdev, 0);\n \ndiff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h\nindex f708355306..a40a7d7cc6 100644\n--- a/include/hw/virtio/virtio-net.h\n+++ b/include/hw/virtio/virtio-net.h\n@@ -218,6 +218,8 @@ struct VirtIONet {\n uint64_t saved_guest_offloads;\n AnnounceTimer announce_timer;\n bool needs_vnet_hdr_swap;\n+ /* Keep backend (e.g. tap) from reading while VM is stopped. */\n+ VMChangeStateEntry *backend_poll_vmstate;\n bool mtu_bypass_backend;\n /* primary failover device is hidden*/\n bool failover_primary_hidden;\n", "prefixes": [ "08/12" ] }