On Fri, Dec 08, 2023 at 10:29:25AM -0800, Kees Cook wrote: > On Thu, Dec 07, 2023 at 05:57:05PM +0300, Alexey Dobriyan wrote: > > On Wed, Dec 06, 2023 at 12:47:27PM -0800, Kees Cook wrote: > > > Can't we have a generic ARCH_AT_PAGE_SHIFT_MASK too? Something like: > > > > > > #ifndef ARCH_AT_PAGE_SHIFT_MASK > > > #define ARCH_AT_PAGE_SHIFT_MASK > > > NEW_AUX_ENT(AT_PAGE_SHIFT_MASK, 1 << PAGE_SHIFT) > > > #endif > > > > > > Or am I misunderstanding something here? > > > > 1) Arch maintainers can opt into this new way to report information at > > their own pace. > > > > 2) AT_PAGE_SHIFT_MASK is about _all_ pagesizes supported by CPU. > > Reporting just one is missing the point. > > > > I'll clarify comment: mmap() support require many things including > > tests for hugetlbfs being mounted, this is about CPU support. > > I significantly prefer APIs not being arch-specific, It will become arch-independent once all relevant archs opt-in. I doubt anyone is writing new software for sparc or alpha. > so I'd prefer we > always include AT_PAGE_SHIFT_MASK. For an architecture that doesn't > define its own ARCH_AT_PAGE_SHIFT_MASK, it's not _inaccurate_ to report > 1 << PAGE_SHIFT, but it might be incomplete. It is inaccurate if ARCH_AT_PAGE_SHIFT_MASK is defined as "_all_ page shift CPU supports". Inaccurate version is called AT_PAGESZ which lists just 1 page size, there is no need for 2 inaccurate APIs.
