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: Wed, 19 Nov 2014 11:00:30 +0800 Message-ID: <546C07CE.2010503@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> <546ABBC5.7030603@redhat.com> <20141118110454.GB21664@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20141118110454.GB21664@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" Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On 11/18/2014 07:04 PM, Michael S. Tsirkin wrote: > On Tue, Nov 18, 2014 at 11:23:49AM +0800, Jason Wang wrote: >> 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. > From experience, second-guessing user always adds maintainance. > >> 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. > That code is common for all drivers, so it was moved to core. > >> There seems no way to get rid of maintaining compatibility, e.g the >> workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support. > Right - because too many hypervisors shipped without it, it's too > much work to fix them all. > No such motivation here, right? > Right, will post the patch that just fail the probe of virtio-net. Thanks