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No, this is not legal. > +void change_pmd_range_notify_secondary_mmus(unsigned long addr, > + struct mmu_notifier_range *range) > +{ > + if (range->start) > + return; > + > + VM_WARN_ON(addr >= range->end); > + range->start = addr; > + mmu_notifier_invalidate_range_start_nonblock(range); > +} The 'nonblock' entry point is advisory, if it fails the caller must not change the mm. Jason