Re: [PATCH 0/3] kasan: Fix ordering between MTE tag colouring and page->flags

[Andrey Konovalov <andreyknvl@gmail.com>]

Hi Catalin,

On Thu, Jun 9, 2022 at 8:32 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> > This would make __GFP_SKIP_KASAN_UNPOISON do two logically unrelated
> > things: skip setting memory tags and reset page tags. This seems
> > weird.
>
> Not entirely weird, it depends on how you look at it. After allocation,
> you expect the accesses to page_address() to work, irrespective of the
> GFP flags. __kasan_unpoison_pages() ensures that the page->flags match
> the written tag without a new GFP flag to set the page->flags. If you
> skip the unpoisoning something should reset the page->flags tag to
> ensure an accessible page_address(). I find it weirder that you need
> another GFP flag to pretty much say 'give me an accessible page'.

Hm, this makes sense.

> As above, my preference would be to avoid a new flag, just wire this up
> to __GFP_SKIP_KASAN_UNPOISON. But if you do want fine-grained control, I
> can add the above.

OK, let's do as you suggest.

Thanks!