From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752290AbaKQK3D (ORCPT ); Mon, 17 Nov 2014 05:29:03 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36381 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751636AbaKQK3C (ORCPT ); Mon, 17 Nov 2014 05:29:02 -0500 Date: Mon, 17 Nov 2014 12:28:49 +0200 From: "Michael S. Tsirkin" To: Cornelia Huck Cc: Jason Wang , rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Wanlong Gao Subject: Re: [PATCH V3 1/2] virtio: introduce methods of sanitizing device features Message-ID: <20141117102848.GH20133@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> <20141117112048.0b0480ff.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141117112048.0b0480ff.cornelia.huck@de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 17, 2014 at 11:20:48AM +0100, Cornelia Huck wrote: > On Mon, 17 Nov 2014 12:11:39 +0200 > "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. > > Unfortunately, this does not ensure that there won't be buggy > hypervisors out there, just as there's buggy hardware floating around. > > > > > 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. > > Good point. Failing probe is still much better than hitting BUG_ONs. > > We'll still need a driver callback, though, that can return an error on > bogus feature bit combinations. Why bother? Just check features at start of probe, and return an error. -- MST