On 21/02/2019 21:06, Kirill A. Shutemov wrote: > 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. Fair enough, I'll have a go and hopefully people will be able to correct it if I make any mistakes - I'm certainly not going to be able to test all architectures myself. Steve
