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=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 2BEC9C64E7A for ; Tue, 1 Dec 2020 13:46:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A213D206F9 for ; Tue, 1 Dec 2020 13:46:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hT+yaKHs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391281AbgLANqx (ORCPT ); Tue, 1 Dec 2020 08:46:53 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:21215 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387897AbgLANqw (ORCPT ); Tue, 1 Dec 2020 08:46:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606830325; 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: in-reply-to:in-reply-to:references:references; bh=7xHtvWJQ1/fVyh+YgQ/Pyo4MEY0S6YBQRsqBb7T9BYY=; b=hT+yaKHsjbAZjfKKQo6QBjTK8EoaHUUvKiFQ/vsOUoY0Tz6L/K7b55lJvWxGx5TOV+RzPy 9Wt3LsszekOwOuFxhXNwTk4Cc9ZcKsllS/jw85lghr+TQZ4OhkfAFQhRxAYlu+jJxRMR9Z XkOm02Rb/P7FuRnrh30zld15RajhaUA= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-434-PodTjBPZNUO2h4LIB_qW-w-1; Tue, 01 Dec 2020 08:45:23 -0500 X-MC-Unique: PodTjBPZNUO2h4LIB_qW-w-1 Received: by mail-wm1-f72.google.com with SMTP id f12so967455wmf.6 for ; Tue, 01 Dec 2020 05:45:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7xHtvWJQ1/fVyh+YgQ/Pyo4MEY0S6YBQRsqBb7T9BYY=; b=oNQrO/CtVc3zjoROdJ5qv/H+dMTIJfEAPs2pFRnf0BRqecZREhQOvuOiY1J/w3pKMH CFwAP/jPbM7pESfKOsAIQKKt5CsJSXT+dxsrvirlERE4uAZLUvOGpg0ROn2Rl6byYoYx QoXCtPoJyPyNf3mGv5YPCuuRm2uSs0C3k1VqgqXWJe3cTWLB/4UCqp/mumlrE65XqMQg AmKW4u0qc4LY/IeyVl6bPJcIfKVO8pd3cVGc4H/Fs94AKNHScGCh7R1u2Ub2L3ImbCTG WgNTRLYDbPrgexnhaG7zFvvAKFV8SMKDbdy9AyvN9zhgB2b2ycoMpBCQ0Ec5IwdPMdXl q9zA== X-Gm-Message-State: AOAM532SRIGHzA54ZUkLw4SbdLikXid8MqY9x35Nl1QUeKP+b6p9il8D s9hWr3AvblVRfkKhd7d1HZC6b+BIEDvUf6vq4Dp1w5s4g0+sxBweN3LVDtE1NgfQGL1lwKQDyzW Ri8mKt/TZ3pvRJKTqk8I/UWeL X-Received: by 2002:a1c:9d16:: with SMTP id g22mr2790499wme.140.1606830322168; Tue, 01 Dec 2020 05:45:22 -0800 (PST) X-Google-Smtp-Source: ABdhPJxhSyPqZvhUzxny7dwUCDyALwWAtH9kC0ElM1LcOobRdWkhrN4pkcblg+Qq+fVN2rZ9fzgDjw== X-Received: by 2002:a1c:9d16:: with SMTP id g22mr2790467wme.140.1606830321828; Tue, 01 Dec 2020 05:45:21 -0800 (PST) Received: from steredhat (host-79-17-248-175.retail.telecomitalia.it. [79.17.248.175]) by smtp.gmail.com with ESMTPSA id n10sm3361269wrv.77.2020.12.01.05.45.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Dec 2020 05:45:21 -0800 (PST) Date: Tue, 1 Dec 2020 14:45:18 +0100 From: Stefano Garzarella To: Stefan Hajnoczi Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , Mike Christie , fam , linux-scsi , Jason Wang , qemu-devel , Linux Virtualization , target-devel , Paolo Bonzini Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201201134518.pwrggkmixpyro4sg@steredhat> References: <20201118113117.GF182763@stefanha-x1.localdomain> <20201119094315-mutt-send-email-mst@kernel.org> <20201120072802-mutt-send-email-mst@kernel.org> <20201201125943.GE585157@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20201201125943.GE585157@stefanha-x1.localdomain> Precedence: bulk List-ID: X-Mailing-List: target-devel@vger.kernel.org On Tue, Dec 01, 2020 at 12:59:43PM +0000, Stefan Hajnoczi wrote: >On Fri, Nov 20, 2020 at 07:31:08AM -0500, Michael S. Tsirkin wrote: >> On Fri, Nov 20, 2020 at 08:45:49AM +0000, Stefan Hajnoczi wrote: >> > On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi wrote: >> > > >> > > On Thu, Nov 19, 2020 at 4:43 PM Mike Christie >> > > wrote: >> > > > >> > > > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote: >> > > > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie >> > > > > wrote: >> > > > >> >> > > > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote: >> > > > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi wrote: >> > > > > struct vhost_run_worker_info { >> > > > > struct timespec *timeout; >> > > > > sigset_t *sigmask; >> > > > > >> > > > > /* List of virtqueues to process */ >> > > > > unsigned nvqs; >> > > > > unsigned vqs[]; >> > > > > }; >> > > > > >> > > > > /* This blocks until the timeout is reached, a signal is received, or >> > > > > the vhost device is destroyed */ >> > > > > int ret = ioctl(vhost_fd, VHOST_RUN_WORKER, &info); >> > > > > >> > > > > As you can see, userspace isn't involved with dealing with the >> > > > > requests. It just acts as a thread donor to the vhost driver. >> > > > > >> > > > > We would want the VHOST_RUN_WORKER calls to be infrequent to avoid the >> > > > > penalty of switching into the kernel, copying in the arguments, etc. >> > > > >> > > > I didn't get this part. Why have the timeout? When the timeout expires, >> > > > does userspace just call right back down to the kernel or does it do >> > > > some sort of processing/operation? >> > > > >> > > > You could have your worker function run from that ioctl wait for a >> > > > signal or a wake up call from the vhost_work/poll functions. >> > > >> > > An optional timeout argument is common in blocking interfaces like >> > > poll(2), recvmmsg(2), etc. >> > > >> > > Although something can send a signal to the thread instead, >> > > implementing that in an application is more awkward than passing a >> > > struct timespec. >> > > >> > > Compared to other blocking calls we don't expect >> > > ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will >> > > rarely be used and can be dropped from the interface. >> > > >> > > BTW the code I posted wasn't a carefully thought out proposal :). The >> > > details still need to be considered and I'm going to be offline for >> > > the next week so maybe someone else can think it through in the >> > > meantime. >> > >> > One final thought before I'm offline for a week. If >> > ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instance >> > then it's hard to support poll-mode (busy waiting) workers because >> > each device instance consumes a whole CPU. If we stick to an interface >> > where the kernel manages the worker threads then it's easier to share >> > workers between devices for polling. >> >> >> Yes that is the reason vhost did its own reason in the first place. >> >> >> I am vaguely thinking about poll(2) or a similar interface, >> which can wait for an event on multiple FDs. > >I can imagine how using poll(2) would work from a userspace perspective, >but on the kernel side I don't think it can be implemented cleanly. >poll(2) is tied to the file_operations->poll() callback and >read/write/error events. Not to mention there isn't a way to substitue >the vhost worker thread function instead of scheduling out the current >thread while waiting for poll fd events. > >But maybe ioctl(VHOST_WORKER_RUN) can do it: > > struct vhost_run_worker_dev { > int vhostfd; /* /dev/vhost-TYPE fd */ > unsigned nvqs; /* number of virtqueues in vqs[] */ > unsigned vqs[]; /* virtqueues to process */ > }; > > struct vhost_run_worker_info { > struct timespec *timeout; > sigset_t *sigmask; > > unsigned ndevices; > struct vhost_run_worker_dev *devices[]; > }; > >In the simple case userspace sets ndevices to 1 and we just handle >virtqueues for the current device. > >In the fancier shared worker thread case the userspace process has the >vhost fds of all the devices it is processing and passes them to >ioctl(VHOST_WORKER_RUN) via struct vhost_run_worker_dev elements. Which fd will be used for this IOCTL? One of the 'vhostfd' or we should create a new /dev/vhost-workers (or something similar)? Maybe the new device will be cleaner and can be reused also for other stuff (I'm thinking about vDPA software devices). > >>From a security perspective it means the userspace thread has access to >all vhost devices (because it has their fds). > >I'm not sure how the mm is supposed to work. The devices might be >associated with different userspace processes (guests) and therefore >have different virtual memory. Maybe in this case we should do something similar to io_uring SQPOLL kthread where kthread_use_mm()/kthread_unuse_mm() is used to switch virtual memory spaces. After writing, I saw that we already do it this in the vhost_worker() in drivers/vhost/vhost.c > >Just wanted to push this discussion along a little further. I'm buried >under emails and probably wont be very active over the next few days. > I think ioctl(VHOST_WORKER_RUN) might be the right way and also maybe the least difficult one. Thanks, Stefano 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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 C16ABC64E7B for ; Tue, 1 Dec 2020 13:46:36 +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 E42F3206E3 for ; Tue, 1 Dec 2020 13:46:35 +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="hT+yaKHs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E42F3206E3 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]:59096 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kk5zG-0007it-LC for qemu-devel@archiver.kernel.org; Tue, 01 Dec 2020 08:46:34 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36594) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kk5yF-0006vF-So for qemu-devel@nongnu.org; Tue, 01 Dec 2020 08:45:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:54249) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kk5yA-0003no-SU for qemu-devel@nongnu.org; Tue, 01 Dec 2020 08:45:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606830325; 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: in-reply-to:in-reply-to:references:references; bh=7xHtvWJQ1/fVyh+YgQ/Pyo4MEY0S6YBQRsqBb7T9BYY=; b=hT+yaKHsjbAZjfKKQo6QBjTK8EoaHUUvKiFQ/vsOUoY0Tz6L/K7b55lJvWxGx5TOV+RzPy 9Wt3LsszekOwOuFxhXNwTk4Cc9ZcKsllS/jw85lghr+TQZ4OhkfAFQhRxAYlu+jJxRMR9Z XkOm02Rb/P7FuRnrh30zld15RajhaUA= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-342-joxKAhqOM-mLOlfsNj4_0w-1; Tue, 01 Dec 2020 08:45:23 -0500 X-MC-Unique: joxKAhqOM-mLOlfsNj4_0w-1 Received: by mail-wr1-f70.google.com with SMTP id u8so1050138wrq.6 for ; Tue, 01 Dec 2020 05:45:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7xHtvWJQ1/fVyh+YgQ/Pyo4MEY0S6YBQRsqBb7T9BYY=; b=Eqf1rYp2ZNEyWGr7TFFwmzjf2ikdeg2ALklB0QLwruMNiTwRxTERjVwwVheTrWsNvY OGVyaBXg+HJ1rCNSkbqecJTj6vJur3Xc7DYWowvHo2egTW86FZdh3NdS5//ffIKKiz5E 0HiZtaStbfw/RoIL7xj/L86grdIGf8YItc9tCYqaqfBoMA8jOm8B545xmYaLJp9XKP3e Yp/JZSuIe0jMi0yqf/KCYCuu6cw+IE97g51DewzB3RMAaEmODJZWe9biDcE/0TlE+pWX nOzZDTicizL3XG1IRjCkIkPFvUXAuKeoMxH/m7sjuIcCLn4BQUMdzxQ0RJK4RwFSlmcw EdaQ== X-Gm-Message-State: AOAM5317khe6fjoxHUzKwawqGA90FFT9qXC+xAvfhhd7zqOrjKZmfPu3 aBPF4KzMhXFDLPk/Vo4UMsvAucZHNKIrwPN2eWUtHfLbCY8VEYDUKjyOz/RdWYQBA3fjgCaZ5r7 z103XFXuhaQcGU68= X-Received: by 2002:a1c:9d16:: with SMTP id g22mr2790502wme.140.1606830322167; Tue, 01 Dec 2020 05:45:22 -0800 (PST) X-Google-Smtp-Source: ABdhPJxhSyPqZvhUzxny7dwUCDyALwWAtH9kC0ElM1LcOobRdWkhrN4pkcblg+Qq+fVN2rZ9fzgDjw== X-Received: by 2002:a1c:9d16:: with SMTP id g22mr2790467wme.140.1606830321828; Tue, 01 Dec 2020 05:45:21 -0800 (PST) Received: from steredhat (host-79-17-248-175.retail.telecomitalia.it. [79.17.248.175]) by smtp.gmail.com with ESMTPSA id n10sm3361269wrv.77.2020.12.01.05.45.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Dec 2020 05:45:21 -0800 (PST) Date: Tue, 1 Dec 2020 14:45:18 +0100 From: Stefano Garzarella To: Stefan Hajnoczi Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201201134518.pwrggkmixpyro4sg@steredhat> References: <20201118113117.GF182763@stefanha-x1.localdomain> <20201119094315-mutt-send-email-mst@kernel.org> <20201120072802-mutt-send-email-mst@kernel.org> <20201201125943.GE585157@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20201201125943.GE585157@stefanha-x1.localdomain> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=sgarzare@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=sgarzare@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.497, 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_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam , linux-scsi , "Michael S. Tsirkin" , Stefan Hajnoczi , Jason Wang , qemu-devel , Linux Virtualization , target-devel , Paolo Bonzini , Mike Christie Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Dec 01, 2020 at 12:59:43PM +0000, Stefan Hajnoczi wrote: >On Fri, Nov 20, 2020 at 07:31:08AM -0500, Michael S. Tsirkin wrote: >> On Fri, Nov 20, 2020 at 08:45:49AM +0000, Stefan Hajnoczi wrote: >> > On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi wrote: >> > > >> > > On Thu, Nov 19, 2020 at 4:43 PM Mike Christie >> > > wrote: >> > > > >> > > > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote: >> > > > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie >> > > > > wrote: >> > > > >> >> > > > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote: >> > > > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi wrote: >> > > > > struct vhost_run_worker_info { >> > > > > struct timespec *timeout; >> > > > > sigset_t *sigmask; >> > > > > >> > > > > /* List of virtqueues to process */ >> > > > > unsigned nvqs; >> > > > > unsigned vqs[]; >> > > > > }; >> > > > > >> > > > > /* This blocks until the timeout is reached, a signal is received, or >> > > > > the vhost device is destroyed */ >> > > > > int ret = ioctl(vhost_fd, VHOST_RUN_WORKER, &info); >> > > > > >> > > > > As you can see, userspace isn't involved with dealing with the >> > > > > requests. It just acts as a thread donor to the vhost driver. >> > > > > >> > > > > We would want the VHOST_RUN_WORKER calls to be infrequent to avoid the >> > > > > penalty of switching into the kernel, copying in the arguments, etc. >> > > > >> > > > I didn't get this part. Why have the timeout? When the timeout expires, >> > > > does userspace just call right back down to the kernel or does it do >> > > > some sort of processing/operation? >> > > > >> > > > You could have your worker function run from that ioctl wait for a >> > > > signal or a wake up call from the vhost_work/poll functions. >> > > >> > > An optional timeout argument is common in blocking interfaces like >> > > poll(2), recvmmsg(2), etc. >> > > >> > > Although something can send a signal to the thread instead, >> > > implementing that in an application is more awkward than passing a >> > > struct timespec. >> > > >> > > Compared to other blocking calls we don't expect >> > > ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will >> > > rarely be used and can be dropped from the interface. >> > > >> > > BTW the code I posted wasn't a carefully thought out proposal :). The >> > > details still need to be considered and I'm going to be offline for >> > > the next week so maybe someone else can think it through in the >> > > meantime. >> > >> > One final thought before I'm offline for a week. If >> > ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instance >> > then it's hard to support poll-mode (busy waiting) workers because >> > each device instance consumes a whole CPU. If we stick to an interface >> > where the kernel manages the worker threads then it's easier to share >> > workers between devices for polling. >> >> >> Yes that is the reason vhost did its own reason in the first place. >> >> >> I am vaguely thinking about poll(2) or a similar interface, >> which can wait for an event on multiple FDs. > >I can imagine how using poll(2) would work from a userspace perspective, >but on the kernel side I don't think it can be implemented cleanly. >poll(2) is tied to the file_operations->poll() callback and >read/write/error events. Not to mention there isn't a way to substitue >the vhost worker thread function instead of scheduling out the current >thread while waiting for poll fd events. > >But maybe ioctl(VHOST_WORKER_RUN) can do it: > > struct vhost_run_worker_dev { > int vhostfd; /* /dev/vhost-TYPE fd */ > unsigned nvqs; /* number of virtqueues in vqs[] */ > unsigned vqs[]; /* virtqueues to process */ > }; > > struct vhost_run_worker_info { > struct timespec *timeout; > sigset_t *sigmask; > > unsigned ndevices; > struct vhost_run_worker_dev *devices[]; > }; > >In the simple case userspace sets ndevices to 1 and we just handle >virtqueues for the current device. > >In the fancier shared worker thread case the userspace process has the >vhost fds of all the devices it is processing and passes them to >ioctl(VHOST_WORKER_RUN) via struct vhost_run_worker_dev elements. Which fd will be used for this IOCTL? One of the 'vhostfd' or we should create a new /dev/vhost-workers (or something similar)? Maybe the new device will be cleaner and can be reused also for other stuff (I'm thinking about vDPA software devices). > >>From a security perspective it means the userspace thread has access to >all vhost devices (because it has their fds). > >I'm not sure how the mm is supposed to work. The devices might be >associated with different userspace processes (guests) and therefore >have different virtual memory. Maybe in this case we should do something similar to io_uring SQPOLL kthread where kthread_use_mm()/kthread_unuse_mm() is used to switch virtual memory spaces. After writing, I saw that we already do it this in the vhost_worker() in drivers/vhost/vhost.c > >Just wanted to push this discussion along a little further. I'm buried >under emails and probably wont be very active over the next few days. > I think ioctl(VHOST_WORKER_RUN) might be the right way and also maybe the least difficult one. 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[79.17.248.175]) by smtp.gmail.com with ESMTPSA id n10sm3361269wrv.77.2020.12.01.05.45.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Dec 2020 05:45:21 -0800 (PST) Date: Tue, 1 Dec 2020 14:45:18 +0100 From: Stefano Garzarella To: Stefan Hajnoczi Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201201134518.pwrggkmixpyro4sg@steredhat> References: <20201118113117.GF182763@stefanha-x1.localdomain> <20201119094315-mutt-send-email-mst@kernel.org> <20201120072802-mutt-send-email-mst@kernel.org> <20201201125943.GE585157@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20201201125943.GE585157@stefanha-x1.localdomain> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=sgarzare@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: fam , linux-scsi , "Michael S. Tsirkin" , qemu-devel , Linux Virtualization , target-devel , Paolo Bonzini , Mike Christie X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Tue, Dec 01, 2020 at 12:59:43PM +0000, Stefan Hajnoczi wrote: >On Fri, Nov 20, 2020 at 07:31:08AM -0500, Michael S. Tsirkin wrote: >> On Fri, Nov 20, 2020 at 08:45:49AM +0000, Stefan Hajnoczi wrote: >> > On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi wrote: >> > > >> > > On Thu, Nov 19, 2020 at 4:43 PM Mike Christie >> > > wrote: >> > > > >> > > > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote: >> > > > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie >> > > > > wrote: >> > > > >> >> > > > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote: >> > > > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi wrote: >> > > > > struct vhost_run_worker_info { >> > > > > struct timespec *timeout; >> > > > > sigset_t *sigmask; >> > > > > >> > > > > /* List of virtqueues to process */ >> > > > > unsigned nvqs; >> > > > > unsigned vqs[]; >> > > > > }; >> > > > > >> > > > > /* This blocks until the timeout is reached, a signal is received, or >> > > > > the vhost device is destroyed */ >> > > > > int ret = ioctl(vhost_fd, VHOST_RUN_WORKER, &info); >> > > > > >> > > > > As you can see, userspace isn't involved with dealing with the >> > > > > requests. It just acts as a thread donor to the vhost driver. >> > > > > >> > > > > We would want the VHOST_RUN_WORKER calls to be infrequent to avoid the >> > > > > penalty of switching into the kernel, copying in the arguments, etc. >> > > > >> > > > I didn't get this part. Why have the timeout? When the timeout expires, >> > > > does userspace just call right back down to the kernel or does it do >> > > > some sort of processing/operation? >> > > > >> > > > You could have your worker function run from that ioctl wait for a >> > > > signal or a wake up call from the vhost_work/poll functions. >> > > >> > > An optional timeout argument is common in blocking interfaces like >> > > poll(2), recvmmsg(2), etc. >> > > >> > > Although something can send a signal to the thread instead, >> > > implementing that in an application is more awkward than passing a >> > > struct timespec. >> > > >> > > Compared to other blocking calls we don't expect >> > > ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will >> > > rarely be used and can be dropped from the interface. >> > > >> > > BTW the code I posted wasn't a carefully thought out proposal :). The >> > > details still need to be considered and I'm going to be offline for >> > > the next week so maybe someone else can think it through in the >> > > meantime. >> > >> > One final thought before I'm offline for a week. If >> > ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instance >> > then it's hard to support poll-mode (busy waiting) workers because >> > each device instance consumes a whole CPU. If we stick to an interface >> > where the kernel manages the worker threads then it's easier to share >> > workers between devices for polling. >> >> >> Yes that is the reason vhost did its own reason in the first place. >> >> >> I am vaguely thinking about poll(2) or a similar interface, >> which can wait for an event on multiple FDs. > >I can imagine how using poll(2) would work from a userspace perspective, >but on the kernel side I don't think it can be implemented cleanly. >poll(2) is tied to the file_operations->poll() callback and >read/write/error events. Not to mention there isn't a way to substitue >the vhost worker thread function instead of scheduling out the current >thread while waiting for poll fd events. > >But maybe ioctl(VHOST_WORKER_RUN) can do it: > > struct vhost_run_worker_dev { > int vhostfd; /* /dev/vhost-TYPE fd */ > unsigned nvqs; /* number of virtqueues in vqs[] */ > unsigned vqs[]; /* virtqueues to process */ > }; > > struct vhost_run_worker_info { > struct timespec *timeout; > sigset_t *sigmask; > > unsigned ndevices; > struct vhost_run_worker_dev *devices[]; > }; > >In the simple case userspace sets ndevices to 1 and we just handle >virtqueues for the current device. > >In the fancier shared worker thread case the userspace process has the >vhost fds of all the devices it is processing and passes them to >ioctl(VHOST_WORKER_RUN) via struct vhost_run_worker_dev elements. Which fd will be used for this IOCTL? One of the 'vhostfd' or we should create a new /dev/vhost-workers (or something similar)? Maybe the new device will be cleaner and can be reused also for other stuff (I'm thinking about vDPA software devices). > >>From a security perspective it means the userspace thread has access to >all vhost devices (because it has their fds). > >I'm not sure how the mm is supposed to work. The devices might be >associated with different userspace processes (guests) and therefore >have different virtual memory. Maybe in this case we should do something similar to io_uring SQPOLL kthread where kthread_use_mm()/kthread_unuse_mm() is used to switch virtual memory spaces. After writing, I saw that we already do it this in the vhost_worker() in drivers/vhost/vhost.c > >Just wanted to push this discussion along a little further. I'm buried >under emails and probably wont be very active over the next few days. > I think ioctl(VHOST_WORKER_RUN) might be the right way and also maybe the least difficult one. Thanks, Stefano _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization