> From: Nicolin Chen <nicol...@nvidia.com> > Sent: Friday, May 16, 2025 2:45 AM > > On Thu, May 15, 2025 at 06:30:27AM +0000, Tian, Kevin wrote: > > > From: Nicolin Chen <nicol...@nvidia.com> > > > Sent: Friday, May 9, 2025 11:03 AM > > > > > > + > > > +/** > > > + * struct iommu_hw_queue_alloc - ioctl(IOMMU_HW_QUEUE_ALLOC) > > > + * @size: sizeof(struct iommu_hw_queue_alloc) > > > + * @flags: Must be 0 > > > + * @viommu_id: Virtual IOMMU ID to associate the HW queue with > > > + * @type: One of enum iommu_hw_queue_type > > > + * @index: The logical index to the HW queue per virtual IOMMU for a > > > multi-queue > > > + * model > > > > I'm thinking of an alternative way w/o having the user to assign index > > and allowing the driver to poke object dependency (next patch). > > > > Let's say the index is internally assigned by the driver. so this cmd is > > just for allowing a hw queue and it's the driver to decide the allocation > > policy, e.g. in ascending order. > > > > Introduce a new flag in viommu_ops to indicate to core that the > > new hw queue should hold a reference to the previous hw queue. > > > > core maintains a last_queue field in viommu. Upon success return > > from @hw_queue_alloc() the core increments the users refcnt of > > last_queue, records the dependency in iommufd_hw_queue struct, > > and update viommu->last_queue. > > > > Then the destroy order is naturally guaranteed. > > I have thought about that too. It's nice that the core can easily > maintain the dependency for the driver. > > But there would still need an out_index to mark each dynamically > allocated queue. So VMM would know where it should map the queue. > > For example, if VMM wants to allocate a queue at its own index=1 > without allocating index=0 first, kernel cannot fail that as VMM > doesn't provide the index. The only way left for kernel would be > to output the allocated queue with index=0 and then wish VMM can > validate it, which doesn't sound safe.. >
VMM's index is virtual which could be mapped to whatever queue object created at its own disposal. the uAPI just requires VMM to remember a sequential list of allocated queue objects and destroy them in reverse order of allocation, instead of in the reverse order of virtual indexes.
