On Fri, Sep 22, 2023 at 07:07:40PM +0100, Robin Murphy wrote: > virtio isn't setting ops->pgsize_bitmap for the sake of direct mappings > either; it sets it once it's discovered any instance, since apparently it's > assuming that all instances must support identical page sizes, and thus once > it's seen one it can work "normally" per the core code's assumptions. It's > also I think the only driver which has a "finalise" bodge but *can* still > properly support map-before-attach, by virtue of having to replay mappings > to every new endpoint anyway. Well it can't quite do that since it doesn't know the geometry - it all is sort of guessing and hoping it doesn't explode on replay. If it knows the geometry it wouldn't need finalize... > > What do you think about something like this to replace > > iommu_create_device_direct_mappings(), that does enforce things > > properly? > > I fail to see how that would make any practical difference. Either the > mappings can be correctly set up in a pagetable *before* the relevant device > is attached to that pagetable, or they can't (if the driver doesn't have > enough information to be able to do so) and we just have to really hope > nothing blows up in the race window between attaching the device to an empty > pagetable and having a second try at iommu_create_device_direct_mappings(). > That's a driver-level issue and has nothing to do with pgsize_bitmap either > way. Except we don't detect this in the core code correctly, that is my point. We should detect the aperture conflict, not pgsize_bitmap to check if it is the first or second try. Jason _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
