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Tsirkin" To: Jason Wang Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, parav@nvidia.com, elic@nvidia.com Subject: Re: [RFC PATCH] vdpa: mandate 1.0 device Message-ID: <20210408115834-mutt-send-email-mst@kernel.org> References: <20210408082648.20145-1-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210408082648.20145-1-jasowang@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 08, 2021 at 04:26:48PM +0800, Jason Wang wrote: > This patch mandates 1.0 for vDPA devices. The goal is to have the > semantic of normative statement in the virtio spec and eliminate the > burden of transitional device for both vDPA bus and vDPA parent. > > uAPI seems fine since all the vDPA parent mandates > VIRTIO_F_ACCESS_PLATFORM which implies 1.0 devices. > > For legacy guests, it can still work since Qemu will mediate when > necessary (e.g doing the endian conversion). > > Signed-off-by: Jason Wang Hmm. If we do this, don't we still have a problem with legacy drivers which don't ack 1.0? Note 1.0 affects ring endianness which is not mediated in QEMU so QEMU can't pretend to device guest is 1.0. > --- > include/linux/vdpa.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h > index 0fefeb976877..cfde4ec999b4 100644 > --- a/include/linux/vdpa.h > +++ b/include/linux/vdpa.h > @@ -6,6 +6,7 @@ > #include > #include > #include > +#include > > /** > * vDPA callback definition. > @@ -317,6 +318,11 @@ static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features) > { > const struct vdpa_config_ops *ops = vdev->config; > > + /* Mandating 1.0 to have semantics of normative statements in > + * the spec. */ > + if (!(features & BIT_ULL(VIRTIO_F_VERSION_1))) > + return -EINVAL; > + > vdev->features_valid = true; > return ops->set_features(vdev, features); > } > -- > 2.25.1