On Thu, Dec 02, 2021 at 09:55:02AM -0400, Jason Gunthorpe wrote: > Further, there is no reason why IMS should be reserved exclusively for > VFIO! Why shouldn't the cdev be able to use IMS vectors too? It is > just a feature of the PCI device like MSI. If the queue has a PASID it > can use IDXD's IMS. No, sorry, but a cdev is not for anything resembling any real resource at all. It is ONLY for the /dev/NODE interface that controls the character device api to userspace. The struct device involved in it is ONLY for that, nothing else. Any attempt to add things to it will be gleefully rejected. The cdev api today (in the kernel) exposes too much mess and there's at least 4 or 5 different ways to use it. It's on my long-term TODO list to fix this up to not even allow abuses like you are considering here, so please don't do that. > If we really need a 2nd struct device to turn on IMS then, I'd suggest > picking the cdev, as it keeps IMS and its allocator inside the IDXD > PCIe driver and not in the VFIO world. No! Again, a cdev is to control the lifespan/lifecycle of the /dev/NODE only. Anything other than that is not ok to do at all. thanks, greg k-h
