Re: [PATCH v9 09/12] mm/kasan: kasan specific map populate function

[Pavel Tatashin]

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.

>> 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

Pavel