iommu/sva: Restore SVA handle sharing
Prior to commit 092edadd ("iommu: Support mm PASID 1:n with sva domains") the code allowed a SVA handle to be bound multiple times to the same (mm, device) pair. This was alluded to in the kdoc comment, but we had understood this to be more a remark about allowing multiple devices, not a literal same-driver re-opening the same SVA. It turns out uacce and idxd were both relying on the core code to handle reference counting for same-device same-mm scenarios. As this looks hard to resolve in the drivers bring it back to the core code. The new design has changed the meaning of the domain->users refcount to refer to the number of devices that are sharing that domain for the same mm. This is part of the design to lift the SVA domain de-duplication out of the drivers. Return the old behavior by explicitly de-duplicating the struct iommu_sva handle. The same (mm, device) will return the same handle pointer and the core code will handle tracking this. The last unbind of the handle will destroy it. Fixes: 092edadd ("iommu: Support mm PASID 1:n with sva domains") Reported-by:Zhangfei Gao <zhangfei.gao@linaro.org> Closes: https://lore.kernel.org/all/20240221110658.529-1-zhangfei.gao@linaro.org/ Tested-by: