From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53928) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f9Bqx-0001U7-5K for qemu-devel@nongnu.org; Thu, 19 Apr 2018 11:52:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f9Bqt-00022S-Gx for qemu-devel@nongnu.org; Thu, 19 Apr 2018 11:52:06 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:45608 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f9Bqt-00022D-Al for qemu-devel@nongnu.org; Thu, 19 Apr 2018 11:52:03 -0400 References: <20180412151232.17506-1-tiwei.bie@intel.com> <20180412151232.17506-7-tiwei.bie@intel.com> <20180418192154-mutt-send-email-mst@kernel.org> <20180419111439.i6gfhnept6wy7uzp@debian> <20180419180912-mutt-send-email-mst@kernel.org> From: Paolo Bonzini Message-ID: <174b5e48-dfde-cb5f-e664-39d43a20a629@redhat.com> Date: Thu, 19 Apr 2018 17:51:51 +0200 MIME-Version: 1.0 In-Reply-To: <20180419180912-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [virtio-dev] RE: [PATCH v3 6/6] vhost-user: support registering external host notifiers List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: "Liang, Cunming" , "Bie, Tiwei" , "jasowang@redhat.com" , "alex.williamson@redhat.com" , "stefanha@redhat.com" , "qemu-devel@nongnu.org" , "virtio-dev@lists.oasis-open.org" , "Daly, Dan" , "Tan, Jianfeng" , "Wang, Zhihong" , "Wang, Xiao W" On 19/04/2018 17:19, Michael S. Tsirkin wrote: >> - if we make it 1 when weak barriers are needed, the device also needs >> to nack feature negotiation (not allow setting the FEATURES_OK) if the >> bit is not set by the driver. >> However, that is not enough. Live >> migration assumes that it is okay to migrate a virtual machine from a >> source that doesn't support a feature to a destination that supports it. >> In this case, it would assume that it is okay to migrate from software >> virtio to hardware virtio. This is wrong because the destination would >> use weak barriers > > You can't migrate between systems with different sets of device features > right now. Yes, you can, exactly because some features are defined not by the machine type but rather by the host kernel. See virtio_net_get_features in QEMU's hw/virtio/virtio-net.c, and virtio_set_features_nocheck in QEMU's hw/virtio/virtio.c. Thanks, Paolo From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-3880-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [66.179.20.138]) by lists.oasis-open.org (Postfix) with ESMTP id 3D37B58191A0 for ; Thu, 19 Apr 2018 08:52:13 -0700 (PDT) References: <20180412151232.17506-1-tiwei.bie@intel.com> <20180412151232.17506-7-tiwei.bie@intel.com> <20180418192154-mutt-send-email-mst@kernel.org> <20180419111439.i6gfhnept6wy7uzp@debian> <20180419180912-mutt-send-email-mst@kernel.org> From: Paolo Bonzini Message-ID: <174b5e48-dfde-cb5f-e664-39d43a20a629@redhat.com> Date: Thu, 19 Apr 2018 17:51:51 +0200 MIME-Version: 1.0 In-Reply-To: <20180419180912-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [virtio-dev] RE: [PATCH v3 6/6] vhost-user: support registering external host notifiers To: "Michael S. Tsirkin" Cc: "Liang, Cunming" , "Bie, Tiwei" , "jasowang@redhat.com" , "alex.williamson@redhat.com" , "stefanha@redhat.com" , "qemu-devel@nongnu.org" , "virtio-dev@lists.oasis-open.org" , "Daly, Dan" , "Tan, Jianfeng" , "Wang, Zhihong" , "Wang, Xiao W" List-ID: On 19/04/2018 17:19, Michael S. Tsirkin wrote: >> - if we make it 1 when weak barriers are needed, the device also needs >> to nack feature negotiation (not allow setting the FEATURES_OK) if the >> bit is not set by the driver. >> However, that is not enough. Live >> migration assumes that it is okay to migrate a virtual machine from a >> source that doesn't support a feature to a destination that supports it. >> In this case, it would assume that it is okay to migrate from software >> virtio to hardware virtio. This is wrong because the destination would >> use weak barriers > > You can't migrate between systems with different sets of device features > right now. Yes, you can, exactly because some features are defined not by the machine type but rather by the host kernel. See virtio_net_get_features in QEMU's hw/virtio/virtio-net.c, and virtio_set_features_nocheck in QEMU's hw/virtio/virtio.c. Thanks, Paolo --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org