On Mon, Oct 09, 2017 at 02:42:32PM -0400, Pavel Tatashin wrote: > Hi Will, > > In addition to what Michal wrote: > > > As an interim step, why not introduce something like > > vmemmap_alloc_block_flags and make the page-table walking opt-out for > > architectures that don't want it? Then we can just pass __GFP_ZERO from > > our vmemmap_populate where necessary and other architectures can do the > > page-table walking dance if they prefer. > > I do not see the benefit, implementing this approach means that we > would need to implement two table walks instead of one: one for x86, > another for ARM, as these two architectures support kasan. Also, this > would become a requirement for any future architecture that want to > add kasan support to add this page table walk implementation. We have two table walks even with your patch series applied afaict: one in our definition of vmemmap_populate (arch/arm64/mm/mmu.c) and this one in the core code. > >> IMO, while I understand that it looks strange that we must walk page > >> table after creating it, it is a better approach: more enclosed as it > >> effects kasan only, and more universal as it is in common code. > > > > I don't buy the more universal aspect, but I appreciate it's subjective. > > Frankly, I'd just sooner not have core code walking early page tables if > > it can be avoided, and it doesn't look hard to avoid it in this case. > > The fact that you're having to add pmd_large and pud_large, which are > > otherwise unused in mm/, is an indication that this isn't quite right imo. > > 28 +#define pmd_large(pmd) pmd_sect(pmd) > 29 +#define pud_large(pud) pud_sect(pud) > > it is just naming difference, ARM64 calls them pmd_sect, common mm and > other arches call them > pmd_large/pud_large. Even the ARM has these defines in > > arm/include/asm/pgtable-3level.h > arm/include/asm/pgtable-2level.h My worry is that these are actually highly arch-specific, but will likely grow more users in mm/ that assume things for all architectures that aren't necessarily valid. Will -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
