[PATCH v6 0/4] arm64: improve efficiency of setting tags for user pages

[Andrew Morton]

On Wed,  2 Jun 2021 16:52:26 -0700 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 avoiding poisoning user pages on free.
> 
> ...
> 
>  arch/alpha/include/asm/page.h   |  6 +--
>  arch/arm64/include/asm/mte.h    |  4 ++
>  arch/arm64/include/asm/page.h   | 10 +++--
>  arch/arm64/lib/mte.S            | 20 ++++++++++
>  arch/arm64/mm/fault.c           | 26 +++++++++++++
>  arch/arm64/mm/proc.S            | 10 +++--
>  arch/ia64/include/asm/page.h    |  6 +--
>  arch/m68k/include/asm/page_no.h |  6 +--
>  arch/s390/include/asm/page.h    |  6 +--
>  arch/x86/include/asm/page.h     |  6 +--
>  include/linux/gfp.h             | 18 +++++++--
>  include/linux/highmem.h         | 43 ++++++++-------------
>  include/linux/kasan.h           | 64 +++++++++++++++++++-------------
>  include/linux/page-flags.h      |  9 +++++
>  include/trace/events/mmflags.h  |  9 ++++-
>  mm/kasan/common.c               |  4 +-
>  mm/kasan/hw_tags.c              | 32 ++++++++++++++++
>  mm/mempool.c                    |  6 ++-
>  mm/page_alloc.c                 | 66 +++++++++++++++++++--------------
>  19 files changed, 242 insertions(+), 109 deletions(-)

This is more MMish than ARMish, but I expect it will get more exposure
in an ARM tree than in linux-next alone.

I'll grab them for now, but in the hope that they will appear in -next
via an ARM tree so I get to drop them again.