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> > +            pgtable_walk_level(m, phys_to_virt(phys_addr), > > Also, obligatory reminder that pfn_valid() only means that pfn_to_page() > gets you a valid struct page. Whether that page is direct-mapped kernel > memory or not is a different matter. Even though this is debugfs, if the operation is sketchy like that and can theortically crash the kernel the driver should test capabilities, CAP_SYS_RAWIO or something may be appropriate. I don't think we have a better cap for 'userspace may crash the kernel' Jason