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[93.172.224.64]) by smtp.gmail.com with ESMTPSA id x13sm6473465ejv.64.2021.10.04.08.05.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Oct 2021 08:05:22 -0700 (PDT) Date: Mon, 4 Oct 2021 11:05:19 -0400 From: "Michael S. Tsirkin" To: Cornelia Huck Subject: Re: [RFC PATCH 1/1] virtio: write back features before verify Message-ID: <20211004110152-mutt-send-email-mst@kernel.org> References: <20210930012049.3780865-1-pasic@linux.ibm.com> <20210930070444-mutt-send-email-mst@kernel.org> <87fstm47no.fsf@redhat.com> <20211002141351-mutt-send-email-mst@kernel.org> <20211003070030.658fc94e.pasic@linux.ibm.com> <20211003021027-mutt-send-email-mst@kernel.org> <20211003032253-mutt-send-email-mst@kernel.org> <87ee912e45.fsf@redhat.com> <20211004083455-mutt-send-email-mst@kernel.org> <878rz83lx0.fsf@redhat.com> MIME-Version: 1.0 In-Reply-To: <878rz83lx0.fsf@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-Disposition: inline Cc: linux-s390@vger.kernel.org, markver@us.ibm.com, Christian Borntraeger , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Halil Pasic , Xie Yongji , virtio-dev@lists.oasis-open.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote: > On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: > > > On Mon, Oct 04, 2021 at 02:01:14PM +0200, Cornelia Huck wrote: > >> On Sun, Oct 03 2021, "Michael S. Tsirkin" wrote: > >> > @@ -160,6 +163,33 @@ \subsection{Legacy Interface: A Note on Feature > >> > Specification text within these sections generally does not apply > >> > to non-transitional devices. > >> > > >> > +\begin{note} > >> > +The device offers different features when used through > >> > +the legacy interface and when operated in accordance with this > >> > +specification. > >> > +\end{note} > >> > + > >> > +Transitional drivers MUST use Devices only through the legacy interface > >> > >> s/Devices only through the legacy interface/devices through the legacy > >> interface only/ > >> > >> ? > > > > Both versions are actually confused, since how do you > > find out that device does not offer VIRTIO_F_VERSION_1? > > > > I think what this should really say is > > > > Transitional drivers MUST NOT accept VIRTIO_F_VERSION_1 through > > the legacy interface. > > Ok, that makes sense. > > Would it make sense that transitional drivers MUST accept VERSION_1 > through the non-legacy interface? Or is that redundant? We already have: A driver MUST accept VIRTIO_F_VERSION_1 if it is offered. > > > > > > Does linux actually satisfy this? Will it accept VIRTIO_F_VERSION_1 > > through the legacy interface if offered? > > I think that the Linux drivers will not operate on feature bit 32+ if > they are in legacy mode? Well ... with PCI there's no *way* for host to set bit 32 through legacy. But it might be possible with MMIO/CCW. Can you tell me what happens then? > >> > >> Generally, looks good to me. > > > > Do we want to also add explanation that features can be > > changed until FEATURES_OK? > > I always considered that to be implict, as feature negotiation is not > over until we have FEATURES_OK. Not sure whether we need an extra note. Well Halil here says once you set a feature bit you can't clear it. So maybe not ... -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization