On Thu, Jun 03, 2021 at 08:03:08PM -0700, Andrew Morton wrote:

On Wed,  2 Jun 2021 16:52:26 -0700 Peter Collingbourne [off-list ref] wrote:

quoted

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.

Sure thing, I'll queue this in a sec...

Peter -- please cc me on patches touching arch/arm64 in future, that way I
won't miss anything (or at least, you can yell at me if I do!).

Cheers,

Will