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Tsirkin" To: David Hildenbrand Cc: Halil Pasic , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, Chandra Merla , Stable@vger.kernel.org, Cornelia Huck , Thomas Huth , Eric Farman , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Wei Wang Subject: Re: [PATCH v1] s390/virtio_ccw: don't allocate/assign airqs for non-existing queues Message-ID: <20250407045456-mutt-send-email-mst@kernel.org> References: <20250404160025.3ab56f60.pasic@linux.ibm.com> <6f548b8b-8c6e-4221-a5d5-8e7a9013f9c3@redhat.com> <20250404173910.6581706a.pasic@linux.ibm.com> <20250407034901-mutt-send-email-mst@kernel.org> <2b187710-329d-4d36-b2e7-158709ea60d6@redhat.com> <20250407042058-mutt-send-email-mst@kernel.org> <0c221abf-de20-4ce3-917d-0375c1ec9140@redhat.com> <20250407044743-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: y7_ebIi45dvVCIBqCqY4xtyxK68qaU3VUWpJmHDOdRU_1744016302 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, Apr 07, 2025 at 10:54:00AM +0200, David Hildenbrand wrote: > On 07.04.25 10:49, Michael S. Tsirkin wrote: > > On Mon, Apr 07, 2025 at 10:44:21AM +0200, David Hildenbrand wrote: > > > > > > > > > > > > > > > > > Whoever adds new feat_X *must be aware* about all previous features, > > > > > otherwise we'd be reusing feature bits and everything falls to pieces. > > > > > > > > > > > > The knowledge is supposed be limited to which feature bit to use. > > > > > > I think we also have to know which virtqueue bits can be used, right? > > > > > > > what are virtqueue bits? vq number? > > Yes, sorry. I got confused myself, it's vq index actually now, we made the spec consistent with that terminology. used to be number/index interchangeably. > Assume cross-vm as an example. It would make use of virtqueue indexes 5+6 > with their VIRTIO_BALLOON_F_WS_REPORTING. crossvm guys really should have reserved the feature bit even if they did not bother specifying it. Let's reserve it now at least? > So whatever feature another device implements couldn't use this feature bit > or these virtqueue indexes. > > (as long the other device never intends to implement > VIRTIO_BALLOON_F_WS_REPORTING, the virtqueue indexes could be reused. But > the spec will also be a mess, because virtqueue indexes could also have > duplicate meanings ... ugh) what do they do with vq indices btw? > -- > Cheers, > > David / dhildenb