From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features Date: Tue, 18 Nov 2014 11:23:49 +0800 Message-ID: <546ABBC5.7030603@redhat.com> References: <1416215838-21700-1-git-send-email-jasowang@redhat.com> <20141117093701.GC20133@redhat.com> <20141117104430.54362e7d.cornelia.huck@de.ibm.com> <20141117101139.GE20133@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20141117101139.GE20133@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" , Cornelia Huck Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On 11/17/2014 06:11 PM, Michael S. Tsirkin wrote: > On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote: >> On Mon, 17 Nov 2014 11:37:01 +0200 >> "Michael S. Tsirkin" wrote: >> >>> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: >>>> Buggy host may advertised buggy host features (a usual case is that host >>>> advertise a feature whose dependencies were missed). In this case, driver >>>> should detect and disable the buggy features by itself. >>>> >>>> This patch introduces driver specific sanitize_features() method which is >>>> called just before features finalizing to detect and disable buggy features >>>> advertised by host. >>>> >>>> Virtio-net will be the first user. >>>> >>>> Cc: Rusty Russell >>>> Cc: Michael S. Tsirkin >>>> Cc: Cornelia Huck >>>> Cc: Wanlong Gao >>>> Signed-off-by: Jason Wang >>> Hmm this conflicts with virtio 1.0 work: we drop >>> features as bitmap there. >> But that's an implementation detail, no? We'll still need a way for the >> driver to sanitize features, and I think this interface works just fine. > Now that you mention it, I don't think we do. > > The spec is quite explicit that devices must not expose invalid > combinations of features. > > Admittedly, BUG_ON isn't very friendly to hypervisors. > > But e.g. failing probe seems better than trying to work around > hypervisor bugs - otherwise we'll be stuck maintaining compatibility > with hypervisors forever. > I'm ok with failing the probe. But it won't cost big effort to workaround only features dependencies issue. I don't see how this block any further features implementation. Looking at virtio-net, it also depends on network core to fix NETIF_F_* dependencies. There seems no way to get rid of maintaining compatibility, e.g the workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support.