[PATCH v3 0/3] arm64: improve efficiency of setting tags for user pages

[Peter Collingbourne]

On Wed, May 12, 2021 at 1:09 PM Peter Collingbourne <pcc at google.com> wrote:
>
> Currently we can end up touching PROT_MTE user pages twice on fault
> and once on unmap. On fault, with KASAN disabled we first clear data
> and then set tags to 0, and with KASAN enabled we simultaneously
> clear data and set tags to the KASAN random tag, and then set tags
> again to 0. On unmap, we poison the page by setting tags, but this
> is less likely to find a bug than poisoning kernel pages.
>
> This patch series fixes these inefficiencies by only touching the pages
> once on fault using the DC GZVA instruction to clear both data and
> tags, and providing the option to avoid poisoning user pages on free.
>
> Peter Collingbourne (3):
>   kasan: use separate (un)poison implementation for integrated init
>   arm64: mte: handle tags zeroing at page allocation time
>   kasan: allow freed user page poisoning to be disabled with HW tags

Thanks Catalin for reviewing patch 2. Could someone on the KASAN side
please take a look at patches 1 and 3?

I imagine that we'll want this series to go in via the mm tree once it's ready.

Peter