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 X-Spam-Level: X-Spam-Status: No, score=-5.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18B30C433DF for ; Mon, 1 Jun 2020 12:52:52 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id D494820679 for ; Mon, 1 Jun 2020 12:52:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Eq/Tkbor" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D494820679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:36634 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jfjvv-0000fL-50 for qemu-devel@archiver.kernel.org; Mon, 01 Jun 2020 08:52:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55298) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jfjvH-00005V-EH for qemu-devel@nongnu.org; Mon, 01 Jun 2020 08:52:11 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:36370 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jfjvG-0006cj-2C for qemu-devel@nongnu.org; Mon, 01 Jun 2020 08:52:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591015928; 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=D9/AjvjTTd1SK5m34QwcPedo4A4TpGLJqi68dsmuOfI=; b=Eq/Tkbor7pSw4GkjJj2uKztjJNbVAbgafEXWNYe6KuaTkcE0PPqkzN2Fte/+xTe0GSQ5wF KwMFmvdtTfmYYK+V0GaLPK+7aBiwq4qSCnaXvBnVzXbVRFntEMOQeEyG4XXix3zzvU1p6R kOaE76CB9oK87BxM3eNM7+J3UBgyza8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-482-feb2DuEgPsWAmCpZCwQgnQ-1; Mon, 01 Jun 2020 08:52:03 -0400 X-MC-Unique: feb2DuEgPsWAmCpZCwQgnQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A2FFA8730EE; Mon, 1 Jun 2020 12:52:02 +0000 (UTC) Received: from [10.72.12.97] (ovpn-12-97.pek2.redhat.com [10.72.12.97]) by smtp.corp.redhat.com (Postfix) with ESMTP id EDD805C1D6; Mon, 1 Jun 2020 12:51:44 +0000 (UTC) Subject: Re: [PATCH 2/5] vhost: involve device backends in feature negotiation To: Stefan Hajnoczi References: <20200522171726.648279-1-stefanha@redhat.com> <20200522171726.648279-3-stefanha@redhat.com> <20200529135641.GC367530@stefanha-x1.localdomain> From: Jason Wang Message-ID: <2edb0864-723a-c8e5-7d49-a73540f9f069@redhat.com> Date: Mon, 1 Jun 2020 20:51:43 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200529135641.GC367530@stefanha-x1.localdomain> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/01 08:52:08 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Laurent Vivier , Thomas Huth , Eduardo Habkost , qemu-block@nongnu.org, "Michael S. Tsirkin" , cohuck@redhat.com, qemu-devel@nongnu.org, Raphael Norwitz , "Gonglei \(Arei\)" , Gerd Hoffmann , Paolo Bonzini , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Fam Zheng , Max Reitz , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/5/29 下午9:56, Stefan Hajnoczi wrote: > On Fri, May 29, 2020 at 03:04:54PM +0800, Jason Wang wrote: >> On 2020/5/23 上午1:17, Stefan Hajnoczi wrote: >>> Many vhost devices in QEMU currently do not involve the device backend >>> in feature negotiation. This seems fine at first glance for device types >>> without their own feature bits (virtio-net has many but other device >>> types have none). >>> >>> This overlooks the fact that QEMU's virtqueue implementation and the >>> device backend's implementation may support different features. QEMU >>> must not report features to the guest that the the device backend >>> doesn't support. >>> >>> For example, QEMU supports VIRTIO 1.1 packed virtqueues while many >>> existing vhost device backends do not. When the user sets packed=on the >>> device backend breaks. This should have been handled gracefully by >>> feature negotiation instead. >>> >>> Introduce vhost_get_default_features() and update all vhost devices in >>> QEMU to involve the device backend in feature negotiation. >>> >>> This patch fixes the following error: >>> >>> $ x86_64-softmmu/qemu-system-x86_64 \ >>> -drive if=virtio,file=test.img,format=raw \ >>> -chardev socket,path=/tmp/vhost-user-blk.sock,id=char0 \ >>> -device vhost-user-blk-pci,chardev=char0,packed=on \ >>> -object memory-backend-memfd,size=1G,share=on,id=ram0 \ >>> -M accel=kvm,memory-backend=ram0 >>> qemu-system-x86_64: Failed to set msg fds. >>> qemu-system-x86_64: vhost VQ 0 ring restore failed: -1: Success (0) >> >> It looks to me this could be fixed simply by adding VIRTIO_F_RING_PACKED >> into user_feature_bits in vhost-user-blk.c. >> >> And for the rest, we need require them to call vhost_get_features() with the >> proper feature bits that needs to be acked by the backend. > There is a backwards-compatibility problem: we cannot call > vhost_get_features() with the full set of feature bits that each device > type supports because existing vhost-user backends don't advertise > features properly. QEMU disables features not advertised by the > vhost-user backend. > > For example, if we add VIRTIO_RING_F_EVENT_IDX then it will always be > disabled for existing libvhost-user backends because they don't > advertise this bit :(. Agree. > > The reason I introduced vhost_get_default_features() is to at least > salvage VIRTIO_F_IOMMU_PLATFORM and VIRTIO_F_RING_PACKED. These bits can > be safely negotiated for all devices. > > Any new transport/vring VIRTIO feature bits can also be added to > vhost_get_default_features() safely. > > If a vhost-user device wants to use device type-specific feature bits > then it really needs to call vhost_get_features() directly as you > suggest. But it's important to check whether existing vhost-user > backends actually advertise them - because if they don't advertise them > but rely on them then we'll break existing backends. > > Would you prefer a different approach? I get you now so I think not. Maybe we need document the expected behavior of VHOST_USER_GET_FEATURES e.g which set of features that must be advertised explicitly. And for the set you mention here, we probably need to add: VIRTIO_F_ORDER_PLATFORM, VIRTIO_F_ANY_LAYOUT (not sure if it was too late). And VIRTIO_F_IN_ORDER > >>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>> index aff98a0ede..f8a144dcd0 100644 >>> --- a/hw/virtio/vhost.c >>> +++ b/hw/virtio/vhost.c >>> @@ -48,6 +48,23 @@ static unsigned int used_memslots; >>> static QLIST_HEAD(, vhost_dev) vhost_devices = >>> QLIST_HEAD_INITIALIZER(vhost_devices); >>> +/* >>> + * Feature bits that device backends must explicitly report. Feature bits not >>> + * listed here maybe set by QEMU without checking with the device backend. >>> + * Ideally all feature bits would be listed here but existing vhost device >>> + * implementations do not explicitly report bits like VIRTIO_F_VERSION_1, so we >>> + * can only assume they are supported. >> >> For most backends, we care about the features for datapath. So this is not >> true at least for networking device, since VIRTIO_F_VERSION_1 have impact on >> the length of vnet header length. > The net device is in good shape and doesn't use vhost_default_feature_bits[]. > > vhost_default_feature_bits[] is for devices that haven't been > negotiating feature bits properly. The goal is start involving them in > feature negotiation without breaking existing backends. > > Would you like me to rephrase this comment in some way? That will be better. > >>> + * >>> + * New feature bits added to the VIRTIO spec should usually be included here >>> + * so that existing vhost device backends that do not support them yet continue >>> + * to work. >> >> It actually depends on the type of backend. >> >> Kernel vhost-net does not validate GSO features since qemu can talk directly >> to TAP and vhost doesn't report those features. But for vhost-user GSO >> features must be validated by qemu since qemu can't see what is behind >> vhost-user. > Maybe the comment should say "New transport/vring feature bits". I'm > thinking about things like VIRTIO_F_RING_PACKED that are not > device-specific but require backend support. > > The GSO features you mentioned are device-specific. Devices that want to > let the backend advertise device-specific features cannot use > vhost_default_feature_bits[]. > >>> + */ >>> +static const int vhost_default_feature_bits[] = { >>> + VIRTIO_F_IOMMU_PLATFORM, >>> + VIRTIO_F_RING_PACKED, >>> + VHOST_INVALID_FEATURE_BIT >>> +}; >>> + >>> bool vhost_has_free_slot(void) >>> { >>> unsigned int slots_limit = ~0U; >>> @@ -1468,6 +1485,11 @@ uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits, >>> return features; >>> } >>> +uint64_t vhost_get_default_features(struct vhost_dev *hdev, uint64_t features) >>> +{ >>> + return vhost_get_features(hdev, vhost_default_feature_bits, features); >>> +} >> >> There's probably no need for a new helper, we can do all these inside >> vhost_get_features(). > Would you prefer: > > extern const int vhost_default_feature_bits[]; > > And then callers do: > > vhost_get_features(hdev, vhost_default_feature_bits, features); > > ? That's fine or maybe just do features |= vhost_default_feature_bits inside vhost_get_features(). Thanks