From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:47606) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RTr4W-0008A0-De for qemu-devel@nongnu.org; Fri, 25 Nov 2011 03:23:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RTr4V-0007my-Eo for qemu-devel@nongnu.org; Fri, 25 Nov 2011 03:23:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:22472) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RTr4V-0007ir-7I for qemu-devel@nongnu.org; Fri, 25 Nov 2011 03:23:47 -0500 Message-ID: <4ECF508E.5050709@redhat.com> Date: Fri, 25 Nov 2011 09:23:42 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1322137732-30840-1-git-send-email-pbonzini@redhat.com> <20111124164203.GE26770@redhat.com> <4ECE7593.5090902@redhat.com> <20111124175436.GA29199@redhat.com> In-Reply-To: <20111124175436.GA29199@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1.0] virtio: add and use virtio_set_features List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, agraf@suse.de On 11/24/2011 06:55 PM, Michael S. Tsirkin wrote: > > Could some backend make it a hard failure? > > I don't see how, there's no way to report a failure from > an io port write. You can exit(1), or fall back to a restricted set of features like we do for BAD_FEATURE. BAD_FEATURE is a special case of features that is not exposed by the host, but requested by the guest. > > If I understand > > correctly, this would have prevented the BAD_FEATURE bug too. > > Which bug? VIRTIO_F_BAD_FEATURE(30) This feature should never be negotiated by the guest; doing so is an indication that the guest is faulty. An experimental virtio PCI driver contained in Linux version 2.6.25 had this problem, and this feature bit can be used to detect it. > what would have prevented it. exit(1) on unsupported features. Paolo