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

[Will Deacon]

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

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