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Tsirkin" To: Cornelia Huck Subject: Re: [PATCH RFC] virtio-fs: force virtio 1.x usage Message-ID: <20200702061631-mutt-send-email-mst@kernel.org> References: <20200629102758.421552-1-cohuck@redhat.com> <20200629104948-mutt-send-email-mst@kernel.org> <20200629173933.35cea40f.cohuck@redhat.com> <20200629114515-mutt-send-email-mst@kernel.org> <20200630113527.7b27f34f.cohuck@redhat.com> <20200630064227-mutt-send-email-mst@kernel.org> <20200630133043.2be1d209.cohuck@redhat.com> <20200630074918-mutt-send-email-mst@kernel.org> <20200701155819.55c64224.cohuck@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200701155819.55c64224.cohuck@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/02 03:23:40 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: 2 X-Spam_score: 0.2 X-Spam_bar: / X-Spam_report: (0.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_SBL_CSS=3.335, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Eric Auger , "Dr. David Alan Gilbert" , Stefan Hajnoczi , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 01, 2020 at 03:58:19PM +0200, Cornelia Huck wrote: > On Tue, 30 Jun 2020 09:02:31 -0400 > "Michael S. Tsirkin" wrote: > > > On Tue, Jun 30, 2020 at 01:30:43PM +0200, Cornelia Huck wrote: > > > On Tue, 30 Jun 2020 06:45:42 -0400 > > > "Michael S. Tsirkin" wrote: > > > > > > > On Tue, Jun 30, 2020 at 11:35:27AM +0200, Cornelia Huck wrote: > > > > > > First, I noticed that virtio-iommu does not force virtio-1, either; I > > > > > think it should? Eric? > > > > > > > > > > Then, there's the mechanism using different names for transitional and > > > > > non-transitional devices. Devices that support both usually define both > > > > > names (with disable_legacy and disable_modern set appropriately) and a > > > > > base name (where the properties can be set manually for the desired > > > > > effect). Most virtio-1 only devices set neither the non-transitional > > > > > nor the transitional name and rely on virtio_pci_force_virtio_1() to > > > > > disable legacy support. But there are outliers: > > > > > > > > > > * this device: it has only a non-transitional name > > > > > ("vhost-user-fs-pci"), which means we automatically get the correct > > > > > configuration; in order to define a transitional/legacy device, you > > > > > would need to use the base name "vhost-user-fs-pci-base" explicitly, > > > > > and it's unlikely that someone has been doing that. > > > > > * virtio-iommu (which I *think* is a virtio-1 only device): it defines > > > > > the full set of transitional, non-transitional, and base names. > > > > > > > > > > How should we proceed? > > > > > * With this patch here, we can fence off the very unlikely possibility > > > > > of somebody configuring a non-modern virtio-fs device for pci. We > > > > > probably should do it, but I don't think we need compat handling. > > > > > * For virtio-iommu, we should get an agreement what the desired state > > > > > is. If it really should be modern only, we need compat handling, as > > > > > the device had been added in 5.0. (And we need to figure out how to > > > > > apply that compat handling.) > > > > > > > > > > > > Well I know it's not really used on x86 yet, so no problem there. > > > > > > > > Which machines are actually affected? > > > > > > I'd suspect ARM, but breaking even a subset is not nice. > > > > OK so MMIO does not have transitional at all right? > > IIRC, yes. > > But I think there are ARM machines that use virtio-pci as well, right? Right :( I guess we do need a compat property for that. -- MST