On Tue, 2015-02-10 at 12:51 -0800, Dave Hansen wrote: > On 02/10/2015 12:42 PM, Toshi Kani wrote: > > On Tue, 2015-02-10 at 10:59 -0800, Dave Hansen wrote: > >> On 02/09/2015 02:45 PM, Toshi Kani wrote: > >>> Implement huge KVA mapping interfaces on x86. Select > >>> HAVE_ARCH_HUGE_VMAP when X86_64 or X86_32 with X86_PAE is set. > >>> Without X86_PAE set, the X86_32 kernel has the 2-level page > >>> tables and cannot provide the huge KVA mappings. > >> > >> Not that it's a big deal, but what's the limitation with the 2-level > >> page tables on 32-bit? We have a 4MB large page size available there > >> and we already use it for the kernel linear mapping. > > > > ioremap() calls arch-neutral ioremap_page_range() to set up I/O mappings > > with PTEs. This patch-set enables ioremap_page_range() to set up PUD & > > PMD mappings. With 2-level page table, I do not think this PUD/PMD > > mapping code works unless we add some special code. > > What actually breaks, though? > > Can't you just disable the pud code via ioremap_pud_enabled()? That's what v1 did, and I found in testing that the PMD mapping code did not work when PAE was unset. I think we need special handling similar to one_md_table_init(), which returns pgd as pmd in case of non-PAE. ioremap_page_range() does not have such handling and I thought it would be worth adding it. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>