On Thu, Feb 21, 2019 at 05:16:46PM +0000, Steven Price wrote: > >> Note that in terms of the new page walking code, these new defines are > >> only used when walking a page table without a VMA (which isn't currently > >> done), so architectures which don't use p?d_large currently will work > >> fine with the generic versions. They only need to provide meaningful > >> definitions when switching to use the walk-without-a-VMA functionality. > > > > How other architectures would know that they need to provide the helpers > > to get walk-without-a-VMA functionality? This looks very fragile to me. > > Yes, you've got a good point there. This would apply to the p?d_large > macros as well - any arch which (inadvertently) uses the generic version > is likely to be fragile/broken. > > I think probably the best option here is to scrap the generic versions > altogether and simply introduce a ARCH_HAS_PXD_LARGE config option which > would enable the new functionality to those arches that opt-in. Do you > think this would be less fragile? These helpers are useful beyond pagewalker. Can we actually do some grinding and make *all* archs to provide correct helpers? Yes, it's tedious, but not that bad. I think we could provide generic helpers for folded levels in <asm-generic/pgtable-nop?d.h> and rest has to be provided by the arch. Architectures that support only 2 level paging would need to provide pgd_large(), with 3 -- pmd_large() and so on. -- Kirill A. Shutemov
