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[79.182.31.92]) by smtp.gmail.com with ESMTPSA id b62sm3440480wmh.38.2020.06.30.06.02.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jun 2020 06:02:34 -0700 (PDT) Date: Tue, 30 Jun 2020 09:02:31 -0400 From: "Michael S. Tsirkin" To: Cornelia Huck Subject: Re: [PATCH RFC] virtio-fs: force virtio 1.x usage Message-ID: <20200630074918-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> MIME-Version: 1.0 In-Reply-To: <20200630133043.2be1d209.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=205.139.110.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/30 03:55:26 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 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, 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 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: > > > On Mon, 29 Jun 2020 11:45:35 -0400 > > > "Michael S. Tsirkin" wrote: > > > > > > > On Mon, Jun 29, 2020 at 05:39:33PM +0200, Cornelia Huck wrote: > > > > > On Mon, 29 Jun 2020 10:53:23 -0400 > > > > > "Michael S. Tsirkin" wrote: > > > > > > > > > > > On Mon, Jun 29, 2020 at 12:27:58PM +0200, Cornelia Huck wrote: > > > > > > > virtio-fs devices are only specified for virtio-1, so it is unclear > > > > > > > how a legacy or transitional device should behave. > > > > > > > > > > > > > > Signed-off-by: Cornelia Huck > > > > > > > --- > > > > > > > > > > > > > > Forcing off legacy now (after the virtio-fs device has already been > > > > > > > available) may have unintended consequences, therefore RFC. > > > > > > > > > > > > > > By default, a virtio-pci device uses 'AUTO' for disable_legacy, which > > > > > > > will resolve to different values based upon which bus the device has > > > > > > > been plugged. Therefore, forcing disable_legacy may result in the same > > > > > > > device or a quite different one. > > > > > > > > > > > > > > Even though pre-virtio-1 behaviour of virtio-fs devices is simply not > > > > > > > specified, toggling disable_legacy will have implications for the BAR > > > > > > > layout, IIRC, and therefore a guest might end up getting a different > > > > > > > device, even if it always used it with virtio-1 anyway. > > > > > > > > > > > > > > Not sure what the best way to solve this problem is. Adding a compat > > > > > > > property for disable_legacy=AUTO may be the right thing to do, but I'm > > > > > > > not quite clear if there are any further implications here. > > > > > > Hnm, I'm a bit confused where to actually set this property... > > > > > > Not a property, just some flag that I'd set in the core, > > and then teach all transports to take that into account. > > I was thinking about compat handling for the disable-legacy property > (struggling a bit with it). Let's figure out if we actually need it. > > > > > > > > > > > > > > Well I notice that this device is not migrateable. > > > > > > So I think that we can just switch it over and be done with it. > > > > > > > > > > Oh, that makes things easier. (I'm wondering if libvirt already > > > > > configures this correctly?) > > > > > > > > > > > > > > > > > > > > > > > > Whatever we do here, we should make sure that the ccw incarnation of > > > > > > > this device indeed forces virtio-1. > > > > > > > > > > > > I agree. I notice that the API virtio_pci_force_virtio_1 turned out > > > > > > to be too fragile. I propose that instead we have a whitelist of > > > > > > devices which can be legacy or transitional. Force rest to modern. > > > > > > > > > > Also, there are further complications because the mechanism is per > > > > > transport, and therefore easy to miss. > > > > > > > > > > bool virtio_legacy_allowed(VirtIODevice *vdev) > > > > > { > > > > > switch (vdev->device_id) { > > > > > case <...>: > > > > > > > > > > return true; > > > > > default: > > > > > return false; > > > > > } > > > > > > > > > > Seems straightforward enough. > > > > > > > > > > > > Agreed. virtio spec has the list. > > > > > > Ok, I've been staring at this a bit, and it's a bit messy for other > > > reasons. > > > > > > 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? > > > > > > > * What is the preferred way to express 'this virtio-pci device is > > > modern only'? Using virtio_pci_force_virtio_1()? Setting the > > > non-transitional name to the obvious name? Both? > > > * We probably still want to have a 'central authority' for whether a > > > device is virtio-1 only or not, so all transports can refer to it. > > > > > > Thoughts? > > > > > > I still think that for the above the best approach is a whitelist > > of legacy virtio IDs. > > I agree, a list of the device types that actually support legacy seems > like the way to go. Making it accessible at the right point in the > device instantiation process is the fiddly bit; but maybe I just need a > break from staring at this. > > > > > > > > > > > > > > > > > > > > > > > > > > --- > > > > > > > hw/virtio/vhost-user-fs-pci.c | 1 + > > > > > > > 1 file changed, 1 insertion(+) > > > > > > > > > > > > > > diff --git a/hw/virtio/vhost-user-fs-pci.c b/hw/virtio/vhost-user-fs-pci.c > > > > > > > index e11c889d82b3..244205edf765 100644 > > > > > > > --- a/hw/virtio/vhost-user-fs-pci.c > > > > > > > +++ b/hw/virtio/vhost-user-fs-pci.c > > > > > > > @@ -44,6 +44,7 @@ static void vhost_user_fs_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp) > > > > > > > vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 2; > > > > > > > } > > > > > > > > > > > > > > + virtio_pci_force_virtio_1(vpci_dev); > > > > > > > qdev_realize(vdev, BUS(&vpci_dev->bus), errp); > > > > > > > } > > > > > > > > > > > > > > -- > > > > > > > 2.25.4 > > > > > > > > > > > >