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 36D77C0015E for ; Wed, 19 Jul 2023 14:28:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qM89u-0008Vm-Oe; Wed, 19 Jul 2023 10:28:06 -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 1qM89t-0008VI-8V for qemu-devel@nongnu.org; Wed, 19 Jul 2023 10:28:05 -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 1qM89r-0004gT-IT for qemu-devel@nongnu.org; Wed, 19 Jul 2023 10:28:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689776883; 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=DGX4QWWm7upD7fb/KrKBJjhHcZLahxgtZGczTIh5tqc=; b=XhCvHCkB+Omi2GFRm9r62WyLFtNO011TuKmgOoatcp4K9SAiDXHG+tVl5KcwAzy75rBYm7 jKTFLCtEvTNYZ7pO7AnccG+YdC/HTbsZxflDPd7XfBQxrkwK5TADS35L628WdOGEFIFn9q XFIz74YAVBaLi5atm3o5g6ciprQLOmA= Received: from mail-lf1-f72.google.com (mail-lf1-f72.google.com [209.85.167.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-53-XvNXR3nMOHeAGQVVo9LAmQ-1; Wed, 19 Jul 2023 10:28:01 -0400 X-MC-Unique: XvNXR3nMOHeAGQVVo9LAmQ-1 Received: by mail-lf1-f72.google.com with SMTP id 2adb3069b0e04-4f3932e595dso6236291e87.1 for ; Wed, 19 Jul 2023 07:28:01 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689776880; x=1692368880; h=content-transfer-encoding:in-reply-to:references:cc:to:from :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=DGX4QWWm7upD7fb/KrKBJjhHcZLahxgtZGczTIh5tqc=; b=BrUh8juJkyyoCfIWziysf5d+Y0SZWgH84F+OuT1sNifPtEyBDX6eMsWglu3QfV7moo ZFi4XaZ81FZiCZ11APjQbVjbfiJCtvUz9XlMs+blRMsmuiOdKqx7hxRKBLF9isneIIKi GOz8/Eyh/eOvvCYPFkmm3Tn9OyiCCPNANx8V2DfGAGp7VbhZpGwGjaUqq69nn3ifUQ6r ILJPbKZXatMuXaC342+9Jr0e2DahWTNfxk4zt4KvQW5ZU6tLzuysLo4pV49Gm4MDNrhn PU5lyNJkSHN7U+9Xoufb9MRjcxxZ215wrSxs17g1c1AbGR3vssDwTJD4xHMDCbG64h5E lgaA== X-Gm-Message-State: ABy/qLbrxMvobu/Z4dqUn720xgw4cP3UoApZ4zg6IKRLm4MsqKnSGn8j eUaa3295yXgWZjCtFbYjNjrNx+CZ3o85u3h8fohjkaEAWzmmU5pWeBJVWgfFZrzj0n2oeTepIs9 yPGeP95LDdlRZGmQ= X-Received: by 2002:a05:6512:78f:b0:4f9:6535:a56 with SMTP id x15-20020a056512078f00b004f965350a56mr40173lfr.26.1689776879746; Wed, 19 Jul 2023 07:27:59 -0700 (PDT) X-Google-Smtp-Source: APBJJlH+jsbGLzDota5nYRlFmpUHfLFxa+K2MT15Iv7PXMdRdj/doGs62rcqiH6f3+9tk86TO9V+gg== X-Received: by 2002:a05:6512:78f:b0:4f9:6535:a56 with SMTP id x15-20020a056512078f00b004f965350a56mr40164lfr.26.1689776879329; Wed, 19 Jul 2023 07:27:59 -0700 (PDT) Received: from ?IPV6:2003:cf:d71a:f311:3075:1f38:7e25:e17a? (p200300cfd71af31130751f387e25e17a.dip0.t-ipconnect.de. [2003:cf:d71a:f311:3075:1f38:7e25:e17a]) by smtp.gmail.com with ESMTPSA id a19-20020aa7cf13000000b00521936fadabsm2757188edy.89.2023.07.19.07.27.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Jul 2023 07:27:58 -0700 (PDT) Message-ID: <0c8e2902-89a0-a9b6-744d-6ab737a0dbb0@redhat.com> Date: Wed, 19 Jul 2023 16:27:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH 6/6] vhost-user: Have reset_status fall back to reset Content-Language: en-US From: Hanna Czenczek To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, "Michael S . Tsirkin" , =?UTF-8?Q?Eugenio_P=c3=a9rez?= , German Maglione References: <20230711155230.64277-1-hreitz@redhat.com> <20230711155230.64277-7-hreitz@redhat.com> <20230718151044.GG44841@fedora> <7ba1e055-e513-1735-5e60-eceb06fe877a@redhat.com> In-Reply-To: <7ba1e055-e513-1735-5e60-eceb06fe877a@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 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=-0.089, 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, 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 19.07.23 16:11, Hanna Czenczek wrote: > On 18.07.23 17:10, Stefan Hajnoczi wrote: >> On Tue, Jul 11, 2023 at 05:52:28PM +0200, Hanna Czenczek wrote: >>> The only user of vhost_user_reset_status() is vhost_dev_stop(), which >>> only uses it as a fall-back to stop the back-end if it does not support >>> SUSPEND.  However, vhost-user's implementation is a no-op unless the >>> back-end supports SET_STATUS. >>> >>> vhost-vdpa's implementation instead just calls >>> vhost_vdpa_reset_device(), implying that it's OK to fully reset the >>> device if SET_STATUS is not supported. >>> >>> To be fair, vhost_vdpa_reset_device() does nothing but to set the >>> status >>> to zero.  However, that may well be because vhost-vdpa has no method >>> besides this to reset a device.  In contrast, vhost-user has >>> RESET_DEVICE and a RESET_OWNER, which can be used instead. >>> >>> While it is not entirely clear from documentation or git logs, from >>> discussions and the order of vhost-user protocol features, it >>> appears to >>> me as if RESET_OWNER originally had no real meaning for vhost-user, and >>> was thus used to signal a device reset to the back-end.  Then, >>> RESET_DEVICE was introduced, to have a well-defined dedicated reset >>> command.  Finally, vhost-user received full STATUS support, including >>> SET_STATUS, so setting the device status to 0 is now the preferred way >>> of resetting a device.  Still, RESET_DEVICE and RESET_OWNER should >>> remain valid as fall-backs. >>> >>> Therefore, have vhost_user_reset_status() fall back to >>> vhost_user_reset_device() if the back-end has no STATUS support. >>> >>> Signed-off-by: Hanna Czenczek >>> --- >>>   hw/virtio/vhost-user.c | 2 ++ >>>   1 file changed, 2 insertions(+) >>> >>> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c >>> index 4507de5a92..53a881ec2a 100644 >>> --- a/hw/virtio/vhost-user.c >>> +++ b/hw/virtio/vhost-user.c >>> @@ -2833,6 +2833,8 @@ static void vhost_user_reset_status(struct >>> vhost_dev *dev) >>>       if (virtio_has_feature(dev->protocol_features, >>>                              VHOST_USER_PROTOCOL_F_STATUS)) { >>>           vhost_user_set_status(dev, 0); >>> +    } else { >>> +        vhost_user_reset_device(dev); >>>       } >>>   } >> Did you check whether DPDK treats setting the status to 0 as equivalent >> to RESET_DEVICE? > > If it doesn’t, what’s even the point of using reset_status? Sorry, I’m being unclear, and I think this may be important because it ties into the question from patch 1, what qemu is even trying to do by running SET_STATUS(0) vhost_dev_stop(), so here’s what gave me the impression that SET_STATUS(0) and RESET_DEVICE should be equivalent: vhost-vdpa.c runs SET_STATUS(0) in a function called vhost_vdpa_reset_device().  This is one thing that gave me the impression that this is about an actual full reset. Another is the whole discussion that we’ve had.  vhost_dev_stop() does not call a `vhost_reset_device()` function, it calls `vhost_reset_status()`.  Still, we were always talking about resetting the device. It doesn’t make sense to me that vDPA would provide no function to fully reset a device, while vhost-user does.  Being able to reset a device sounds vital to me.  This also gave me the impression that SET_STATUS(0) on vDPA at least is functionally equivalent to a full device reset. Maybe SET_STATUS(0) does mean a full device reset on vDPA, but not on vhost-user.  That would be a real shame, so I assumed this would not be the case; that SET_STATUS(0) does the same thing on both protocols. The virtio specification says “Writing 0 into this field resets the device.” about the device_status field. This also makes sense, because the device_status field is basically used to tell the device that a driver has taken control.  If reset, this indicates the driver has given up control, and to me this is a point where a device should fully reset itself. So all in all, I can’t see the rationale why any implementation that supports SET_STATUS would decide to treat SET_STATUS(0) not as equivalent or a superset of RESET_DEVICE.  I may be wrong, and this might explain a whole deal about what kind of background operations we hope to stop with SET_STATUS(0). Hanna