From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-3882-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 C2D4058191A0 for ; Thu, 19 Apr 2018 08:59:55 -0700 (PDT) Date: Thu, 19 Apr 2018 18:59:40 +0300 From: "Michael S. Tsirkin" Message-ID: <20180419185630-mutt-send-email-mst@kernel.org> 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> <174b5e48-dfde-cb5f-e664-39d43a20a629@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <174b5e48-dfde-cb5f-e664-39d43a20a629@redhat.com> Subject: Re: [virtio-dev] RE: [PATCH v3 6/6] vhost-user: support registering external host notifiers To: Paolo Bonzini 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 Thu, Apr 19, 2018 at 05:51:51PM +0200, Paolo Bonzini wrote: > 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 Oh you are right. Well we can just special-case that one :) -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org