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Tsirkin" To: Stefano Garzarella Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, Jason Wang , Eugenio =?iso-8859-1?Q?P=E9rez?= , Tiwei Bie , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vhost-vdpa: filter VIRTIO_F_RING_PACKED feature Message-ID: <20230605085840-mutt-send-email-mst@kernel.org> References: <20230605110644.151211-1-sgarzare@redhat.com> <20230605084104-mutt-send-email-mst@kernel.org> <24fjdwp44hovz3d3qkzftmvjie45er3g3boac7aezpvzbwvuol@lmo47ydvnqau> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <24fjdwp44hovz3d3qkzftmvjie45er3g3boac7aezpvzbwvuol@lmo47ydvnqau> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Mon, Jun 05, 2023 at 02:54:20PM +0200, Stefano Garzarella wrote: > On Mon, Jun 05, 2023 at 08:41:54AM -0400, Michael S. Tsirkin wrote: > > On Mon, Jun 05, 2023 at 01:06:44PM +0200, Stefano Garzarella wrote: > > > vhost-vdpa IOCTLs (eg. VHOST_GET_VRING_BASE, VHOST_SET_VRING_BASE) > > > don't support packed virtqueue well yet, so let's filter the > > > VIRTIO_F_RING_PACKED feature for now in vhost_vdpa_get_features(). > > > > > > This way, even if the device supports it, we don't risk it being > > > negotiated, then the VMM is unable to set the vring state properly. > > > > > > Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Stefano Garzarella > > > --- > > > > > > Notes: > > > This patch should be applied before the "[PATCH v2 0/3] vhost_vdpa: > > > better PACKED support" series [1] and backported in stable branches. > > > > > > We can revert it when we are sure that everything is working with > > > packed virtqueues. > > > > > > Thanks, > > > Stefano > > > > > > [1] https://lore.kernel.org/virtualization/20230424225031.18947-1-shannon.nelson@amd.com/ > > > > I'm a bit lost here. So why am I merging "better PACKED support" then? > > To really support packed virtqueue with vhost-vdpa, at that point we would > also have to revert this patch. > > I wasn't sure if you wanted to queue the series for this merge window. > In that case do you think it is better to send this patch only for stable > branches? > > Does this patch make them a NOP? > > Yep, after applying the "better PACKED support" series and being sure that > the IOCTLs of vhost-vdpa support packed virtqueue, we should revert this > patch. > > Let me know if you prefer a different approach. > > I'm concerned that QEMU uses vhost-vdpa IOCTLs thinking that the kernel > interprets them the right way, when it does not. > > Thanks, > Stefano > If this fixes a bug can you add Fixes tags to each of them? Then it's ok to merge in this window. Probably easier than the elaborate mask/unmask dance. > > > > > drivers/vhost/vdpa.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c > > > index 8c1aefc865f0..ac2152135b23 100644 > > > --- a/drivers/vhost/vdpa.c > > > +++ b/drivers/vhost/vdpa.c > > > @@ -397,6 +397,12 @@ static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep) > > > > > > features = ops->get_device_features(vdpa); > > > > > > + /* > > > + * IOCTLs (eg. VHOST_GET_VRING_BASE, VHOST_SET_VRING_BASE) don't support > > > + * packed virtqueue well yet, so let's filter the feature for now. > > > + */ > > > + features &= ~BIT_ULL(VIRTIO_F_RING_PACKED); > > > + > > > if (copy_to_user(featurep, &features, sizeof(features))) > > > return -EFAULT; > > > > > > > > > base-commit: 9561de3a55bed6bdd44a12820ba81ec416e705a7 > > > -- > > > 2.40.1 > >