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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A0FA9C77B71 for ; Thu, 13 Apr 2023 07:18:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pmrDQ-0000di-Ld; Thu, 13 Apr 2023 03:17:57 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pmrDH-0000dQ-2J for qemu-devel@nongnu.org; Thu, 13 Apr 2023 03:17:47 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pmrDE-0007mx-P9 for qemu-devel@nongnu.org; Thu, 13 Apr 2023 03:17:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681370262; 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=+3fxlYnLZG+HH++RdfgY9Ofj5y9sdQsGEkzklrhBFiw=; b=YIYOlP4aNzXuncnT9LCg4MWyipM2dpuPlyZAoXurd+31v8/Dff/k1cnRT3AcC25066wG7X uci7otyq/XjxgMiXzL2yGshaeR8fR7EmQAECIg/c72caemvmEzZOjwvryHRhTJloC8neOg s0s7+y11msCCQ05ngeaxjWTyRbjT68M= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-137-jDIomZs9O3a5PXNDkcAkew-1; Thu, 13 Apr 2023 03:17:39 -0400 X-MC-Unique: jDIomZs9O3a5PXNDkcAkew-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3F9CC1C189A3; Thu, 13 Apr 2023 07:17:39 +0000 (UTC) Received: from [10.39.208.7] (unknown [10.39.208.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5A6AEC16028; Thu, 13 Apr 2023 07:17:18 +0000 (UTC) Message-ID: <74a20bbf-860e-ed5b-03fa-6f25ce865652@redhat.com> Date: Thu, 13 Apr 2023 09:17:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Content-Language: en-US To: Stefan Hajnoczi , Hanna Czenczek Cc: qemu-devel@nongnu.org, virtio-fs@redhat.com, German Maglione , Anton Kuchin , Juan Quintela , "Michael S . Tsirkin" , Stefano Garzarella , Roman Kagan , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= References: <20230411150515.14020-1-hreitz@redhat.com> <20230411150515.14020-2-hreitz@redhat.com> <20230412205138.GA2813183@fedora> From: Maxime Coquelin Subject: Re: [PATCH 1/4] vhost: Re-enable vrings after setting features In-Reply-To: <20230412205138.GA2813183@fedora> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.129.124; envelope-from=maxime.coquelin@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.083, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 4/12/23 22:51, Stefan Hajnoczi wrote: > On Tue, Apr 11, 2023 at 05:05:12PM +0200, Hanna Czenczek wrote: >> If the back-end supports the VHOST_USER_F_PROTOCOL_FEATURES feature, >> setting the vhost features will set this feature, too. Doing so >> disables all vrings, which may not be intended. >> >> For example, enabling or disabling logging during migration requires >> setting those features (to set or unset VHOST_F_LOG_ALL), which will >> automatically disable all vrings. In either case, the VM is running >> (disabling logging is done after a failed or cancelled migration, and >> only once the VM is running again, see comment in >> memory_global_dirty_log_stop()), so the vrings should really be enabled. >> As a result, the back-end seems to hang. >> >> To fix this, we must remember whether the vrings are supposed to be >> enabled, and, if so, re-enable them after a SET_FEATURES call that set >> VHOST_USER_F_PROTOCOL_FEATURES. >> >> It seems less than ideal that there is a short period in which the VM is >> running but the vrings will be stopped (between SET_FEATURES and >> SET_VRING_ENABLE). To fix this, we would need to change the protocol, >> e.g. by introducing a new flag or vhost-user protocol feature to disable >> disabling vrings whenever VHOST_USER_F_PROTOCOL_FEATURES is set, or add >> new functions for setting/clearing singular feature bits (so that >> F_LOG_ALL can be set/cleared without touching F_PROTOCOL_FEATURES). >> >> Even with such a potential addition to the protocol, we still need this >> fix here, because we cannot expect that back-ends will implement this >> addition. >> >> Signed-off-by: Hanna Czenczek >> --- >> include/hw/virtio/vhost.h | 10 ++++++++++ >> hw/virtio/vhost.c | 13 +++++++++++++ >> 2 files changed, 23 insertions(+) >> >> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h >> index a52f273347..2fe02ed5d4 100644 >> --- a/include/hw/virtio/vhost.h >> +++ b/include/hw/virtio/vhost.h >> @@ -90,6 +90,16 @@ struct vhost_dev { >> int vq_index_end; >> /* if non-zero, minimum required value for max_queues */ >> int num_queues; >> + >> + /* >> + * Whether the virtqueues are supposed to be enabled (via >> + * SET_VRING_ENABLE). Setting the features (e.g. for >> + * enabling/disabling logging) will disable all virtqueues if >> + * VHOST_USER_F_PROTOCOL_FEATURES is set, so then we need to >> + * re-enable them if this field is set. >> + */ >> + bool enable_vqs; >> + >> /** >> * vhost feature handling requires matching the feature set >> * offered by a backend which may be a subset of the total >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >> index a266396576..cbff589efa 100644 >> --- a/hw/virtio/vhost.c >> +++ b/hw/virtio/vhost.c >> @@ -50,6 +50,8 @@ static unsigned int used_memslots; >> static QLIST_HEAD(, vhost_dev) vhost_devices = >> QLIST_HEAD_INITIALIZER(vhost_devices); >> >> +static int vhost_dev_set_vring_enable(struct vhost_dev *hdev, int enable); >> + >> bool vhost_has_free_slot(void) >> { >> unsigned int slots_limit = ~0U; >> @@ -899,6 +901,15 @@ static int vhost_dev_set_features(struct vhost_dev *dev, >> } >> } >> >> + if (dev->enable_vqs) { >> + /* >> + * Setting VHOST_USER_F_PROTOCOL_FEATURES would have disabled all >> + * virtqueues, even if that was not intended; re-enable them if >> + * necessary. >> + */ >> + vhost_dev_set_vring_enable(dev, true); >> + } >> + >> out: >> return r; >> } >> @@ -1896,6 +1907,8 @@ int vhost_dev_get_inflight(struct vhost_dev *dev, uint16_t queue_size, >> >> static int vhost_dev_set_vring_enable(struct vhost_dev *hdev, int enable) >> { >> + hdev->enable_vqs = enable; >> + >> if (!hdev->vhost_ops->vhost_set_vring_enable) { >> return 0; >> } > > The vhost-user spec doesn't say that VHOST_F_LOG_ALL needs to be toggled > at runtime and I don't think VHOST_USER_SET_PROTOCOL_FEATURES is > intended to be used like that. This issue shows why doing so is a bad > idea. > > VHOST_F_LOG_ALL does not need to be toggled to control logging. Logging > is controlled at runtime by the presence of the dirty log > (VHOST_USER_SET_LOG_BASE) and the per-vring logging flag > (VHOST_VRING_F_LOG). > > I suggest permanently enabling VHOST_F_LOG_ALL upon connection when the > the backend supports it. No spec changes are required. > > libvhost-user looks like it will work. I didn't look at DPDK/SPDK, but > checking that it works there is important too. > > I have CCed people who may be interested in this issue. This is the > first time I've looked at vhost-user logging, so this idea may not work. In the case of DPDK, we rely on VHOST_F_LOG_ALL to be set to know whether we should do dirty pages logging or not [0], so setting this feature at init time will cause performance degradation. The check on whether the log base address has been set is done afterwards. Regards, Maxime > Stefan [0]: https://git.dpdk.org/dpdk/tree/lib/vhost/vhost.h#n594