[PATCH v2 hmm 01/11] mm/hmm: fix use after free with struct hmm in the mmu notifiers

[Christoph Hellwig]

I still think sruct hmm should die.  We already have a structure used
for additional information for drivers having crazly tight integration
into the VM, and it is called struct mmu_notifier_mm.  We really need
to reuse that intead of duplicating it badly.