!!! This is a first cut, and there are still cleanups to be done in various areas touched by that code. I also haven't done descriptions yet for the individual patches.
The current get_unmapped_area code calls the f_ops->get_unmapped_area or the arch one (via the mm) only when MAP_FIXED is not passed. That makes it impossible for archs to impose proper constraints on regions of the virtual address space. To work around that, get_unmapped_area() then calls some hugetlbfs specific hacks. This cause several problems, among others: - It makes it impossible for a driver or filesystem to do the same thing that hugetlbfs does (for example, to allow a driver to use larger page sizes to map external hardware) if that requires applying a constraint on the addresses (constraining that mapping in certain regions and other mappings out of those regions). - Some archs like arm, mips, sparc, sparc64, sh and sh64 already want MAP_FIXED to be passed down in order to deal with aliasing issues. The code is there to handle it... but is never called. This serie of patches moves the logic to handle MAP_FIXED down to the various arch/driver get_unmapped_area() implementations, and then changes the generic code to always call them. The hugetlbfs hacks then disappear from the generic code. Since I need to do some special 64K pages mappings for SPEs on cell, I need to work around the first problem at least. I have further patches thus implementing a "slices" layer that handles multiple page sizes through slices of the address space for use by hugetlbfs, the SPE code, and possibly others, but it requires that serie of patches first/ There is still a potential (but not practical) issue due to the fact that filesystems/drivers implemeting g_u_a will effectively bypass all arch checks. This is not an issue in practice as the only users of those are actually doing so are doing it using arch hooks in the first place. There is also a problem with mremap that will completely bypass all arch checks. I'll try to address that separately mostly by making it not work when the vma has a file whose f_ops has a get_unmapped_area callback, and by making it use is_hugepage_only_range() before expanding into a new area. Also, I want to turn is_hugepage_only_range() into a more generic is_normal_page_range() as that's really what it will end up meaning when used in stack grow, brk grow and mremap. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
