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 337D1C77B76 for ; Mon, 17 Apr 2023 19:34:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1poUbR-0003t4-Rg; Mon, 17 Apr 2023 15:33:30 -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 1poUbP-0003sv-IK for qemu-devel@nongnu.org; Mon, 17 Apr 2023 15:33:27 -0400 Received: from mail-yb1-xb34.google.com ([2607:f8b0:4864:20::b34]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1poUbN-0002N0-Pi for qemu-devel@nongnu.org; Mon, 17 Apr 2023 15:33:27 -0400 Received: by mail-yb1-xb34.google.com with SMTP id n17so169613ybq.2 for ; Mon, 17 Apr 2023 12:33:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1681760004; x=1684352004; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=C4jc7kY4hMOKIb7LeRwCztF6vfL7uf5k0IumTcQQepY=; b=rCR5CD2robkihYNsuZKsRRxjNMKjI3baF4qaDe+tktHHAZMA7974i4E/LJ+z2vN7Qk LIZwB+dzh9msk2Ac3NMtm/MSw6ef4BHWNN40lqle6f4SaX5f2x36iFThYE1TFNDE47jf Iwx2SlcjyGkIZehZ72b5pyhl7SH53VPP+YKtwtAK7zqLwyaclcbSDn7UlmtkxHIlJdJa fqIcCC6J0BzLkyg/aXVTtrD/5zM8Vj9XoVOUa5Z0QK4WYFORbRbcMSzskktIbBTPSi3/ 8z7HVpOPKLKGeZU9PK0pikgazXSUrVgj3Pe5h9nKMhQm/0gfQGF387DTe6SXazSTxBZh 6W9Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1681760004; x=1684352004; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=C4jc7kY4hMOKIb7LeRwCztF6vfL7uf5k0IumTcQQepY=; b=A2kAZaQHKN9V6IimMiu7Ew/9bXXgZwMSwUU9LDsuPoib5mHz2In3GdeGVQy5WDBQgL aSWKOMSjv59YqL0rpdU2qO7dAybdojPnxjmsBKLFNg3br2Fq5gzrCy5Zmk7o2UDu5V7x P6YzeJHLtJgVZhah8F6lAhL8RWY+SL6NrhhsSBoDZn/rdDhDiXcuq2LdemlFXmBsDaem y3qd/AwViCs1dxGre+jg4/Rc5K2+CDQ+Fj8mNBM0vvb89pZv7/UZb6gXSNnWcSEkX0S4 dPmTmmlEg/mK6bzY/1rugA/mwS4fQ5/bl4u/K1bHKoNnSqTQu2jZT9b0v1SkcgTnoj1+ ns+A== X-Gm-Message-State: AAQBX9fwZC/ohbw+C1GLapfv9WLMysUfhH1pCeG/Ry3fh/kOpnyds+qt ToMD63arrGKU/HQz4ODN/NrmqcAWpJhmBKyeZZI= X-Google-Smtp-Source: AKy350YVcVf7ni5pecekcc4NVl2xDpwik3nu1YbpJI247F3w8YOvu7DyOGR1dUb/mbTrvOdlfYRpTXYusOCSiVMvNJg= X-Received: by 2002:a25:cc97:0:b0:b92:570c:57a1 with SMTP id l145-20020a25cc97000000b00b92570c57a1mr2613356ybf.2.1681760004409; Mon, 17 Apr 2023 12:33:24 -0700 (PDT) MIME-Version: 1.0 References: <20230411150515.14020-1-hreitz@redhat.com> <20230411150515.14020-3-hreitz@redhat.com> <20230412210641.GC2813183@fedora> <20230417153810.GE3852722@fedora> In-Reply-To: From: Stefan Hajnoczi Date: Mon, 17 Apr 2023 15:33:12 -0400 Message-ID: Subject: Re: [PATCH 2/4] vhost-user: Interface for migration state transfer To: Eugenio Perez Martin Cc: Stefan Hajnoczi , Hanna Czenczek , qemu-devel@nongnu.org, virtio-fs@redhat.com, German Maglione , Anton Kuchin , Juan Quintela , "Michael S . Tsirkin" , Stefano Garzarella Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2607:f8b0:4864:20::b34; envelope-from=stefanha@gmail.com; helo=mail-yb1-xb34.google.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Mon, 17 Apr 2023 at 15:10, Eugenio Perez Martin wr= ote: > > On Mon, Apr 17, 2023 at 5:38=E2=80=AFPM Stefan Hajnoczi wrote: > > > > On Thu, Apr 13, 2023 at 12:14:24PM +0200, Eugenio Perez Martin wrote: > > > On Wed, Apr 12, 2023 at 11:06=E2=80=AFPM Stefan Hajnoczi wrote: > > > > > > > > On Tue, Apr 11, 2023 at 05:05:13PM +0200, Hanna Czenczek wrote: > > > > > So-called "internal" virtio-fs migration refers to transporting t= he > > > > > back-end's (virtiofsd's) state through qemu's migration stream. = To do > > > > > this, we need to be able to transfer virtiofsd's internal state t= o and > > > > > from virtiofsd. > > > > > > > > > > Because virtiofsd's internal state will not be too large, we beli= eve it > > > > > is best to transfer it as a single binary blob after the streamin= g > > > > > phase. Because this method should be useful to other vhost-user > > > > > implementations, too, it is introduced as a general-purpose addit= ion to > > > > > the protocol, not limited to vhost-user-fs. > > > > > > > > > > These are the additions to the protocol: > > > > > - New vhost-user protocol feature VHOST_USER_PROTOCOL_F_MIGRATORY= _STATE: > > > > > This feature signals support for transferring state, and is add= ed so > > > > > that migration can fail early when the back-end has no support. > > > > > > > > > > - SET_DEVICE_STATE_FD function: Front-end and back-end negotiate = a pipe > > > > > over which to transfer the state. The front-end sends an FD to= the > > > > > back-end into/from which it can write/read its state, and the b= ack-end > > > > > can decide to either use it, or reply with a different FD for t= he > > > > > front-end to override the front-end's choice. > > > > > The front-end creates a simple pipe to transfer the state, but = maybe > > > > > the back-end already has an FD into/from which it has to write/= read > > > > > its state, in which case it will want to override the simple pi= pe. > > > > > Conversely, maybe in the future we find a way to have the front= -end > > > > > get an immediate FD for the migration stream (in some cases), i= n which > > > > > case we will want to send this to the back-end instead of creat= ing a > > > > > pipe. > > > > > Hence the negotiation: If one side has a better idea than a pla= in > > > > > pipe, we will want to use that. > > > > > > > > > > - CHECK_DEVICE_STATE: After the state has been transferred throug= h the > > > > > pipe (the end indicated by EOF), the front-end invokes this fun= ction > > > > > to verify success. There is no in-band way (through the pipe) = to > > > > > indicate failure, so we need to check explicitly. > > > > > > > > > > Once the transfer pipe has been established via SET_DEVICE_STATE_= FD > > > > > (which includes establishing the direction of transfer and migrat= ion > > > > > phase), the sending side writes its data into the pipe, and the r= eading > > > > > side reads it until it sees an EOF. Then, the front-end will che= ck for > > > > > success via CHECK_DEVICE_STATE, which on the destination side inc= ludes > > > > > checking for integrity (i.e. errors during deserialization). > > > > > > > > > > Suggested-by: Stefan Hajnoczi > > > > > Signed-off-by: Hanna Czenczek > > > > > --- > > > > > include/hw/virtio/vhost-backend.h | 24 +++++ > > > > > include/hw/virtio/vhost.h | 79 ++++++++++++++++ > > > > > hw/virtio/vhost-user.c | 147 ++++++++++++++++++++++++= ++++++ > > > > > hw/virtio/vhost.c | 37 ++++++++ > > > > > 4 files changed, 287 insertions(+) > > > > > > > > > > diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virti= o/vhost-backend.h > > > > > index ec3fbae58d..5935b32fe3 100644 > > > > > --- a/include/hw/virtio/vhost-backend.h > > > > > +++ b/include/hw/virtio/vhost-backend.h > > > > > @@ -26,6 +26,18 @@ typedef enum VhostSetConfigType { > > > > > VHOST_SET_CONFIG_TYPE_MIGRATION =3D 1, > > > > > } VhostSetConfigType; > > > > > > > > > > +typedef enum VhostDeviceStateDirection { > > > > > + /* Transfer state from back-end (device) to front-end */ > > > > > + VHOST_TRANSFER_STATE_DIRECTION_SAVE =3D 0, > > > > > + /* Transfer state from front-end to back-end (device) */ > > > > > + VHOST_TRANSFER_STATE_DIRECTION_LOAD =3D 1, > > > > > +} VhostDeviceStateDirection; > > > > > + > > > > > +typedef enum VhostDeviceStatePhase { > > > > > + /* The device (and all its vrings) is stopped */ > > > > > + VHOST_TRANSFER_STATE_PHASE_STOPPED =3D 0, > > > > > +} VhostDeviceStatePhase; > > > > > > > > vDPA has: > > > > > > > > /* Suspend a device so it does not process virtqueue requests any= more > > > > * > > > > * After the return of ioctl the device must preserve all the nec= essary state > > > > * (the virtqueue vring base plus the possible device specific st= ates) that is > > > > * required for restoring in the future. The device must not chan= ge its > > > > * configuration after that point. > > > > */ > > > > #define VHOST_VDPA_SUSPEND _IO(VHOST_VIRTIO, 0x7D) > > > > > > > > /* Resume a device so it can resume processing virtqueue requests > > > > * > > > > * After the return of this ioctl the device will have restored a= ll the > > > > * necessary states and it is fully operational to continue proce= ssing the > > > > * virtqueue descriptors. > > > > */ > > > > #define VHOST_VDPA_RESUME _IO(VHOST_VIRTIO, 0x7E) > > > > > > > > I wonder if it makes sense to import these into vhost-user so that = the > > > > difference between kernel vhost and vhost-user is minimized. It's o= kay > > > > if one of them is ahead of the other, but it would be nice to avoid > > > > overlapping/duplicated functionality. > > > > > > > > > > That's what I had in mind in the first versions. I proposed VHOST_STO= P > > > instead of VHOST_VDPA_STOP for this very reason. Later it did change > > > to SUSPEND. > > > > I noticed QEMU only calls ioctl(VHOST_VDPA_SUSPEND) and not > > ioctl(VHOST_VDPA_RESUME). > > > > The doc comments in don't explain how the device can > > leave the suspended state. Can you clarify this? > > > > Do you mean in what situations or regarding the semantics of _RESUME? > > To me resume is an operation mainly to resume the device in the event > of a VM suspension, not a migration. It can be used as a fallback code > in some cases of migration failure though, but it is not currently > used in qemu. Is a "VM suspension" the QEMU HMP 'stop' command? I guess the reason why QEMU doesn't call RESUME anywhere is that it resets the device in vhost_dev_stop()? Does it make sense to combine SUSPEND and RESUME with Hanna's SET_DEVICE_STATE_FD? For example, non-iterative migration works like this: - Saving the device's state is done by SUSPEND followed by SET_DEVICE_STATE_FD. If the guest needs to continue executing (e.g. savevm command or migration failed), then RESUME is called to continue. - Loading the device's state is done by SUSPEND followed by SET_DEVICE_STATE_FD, followed by RESUME. Stefan