[PATCH 3/3] arm64: kasan: mte: remove redundant mte_report_once logic

[Andrey Konovalov]

On Sat, Jul 31, 2021 at 12:44 PM Catalin Marinas
<catalin.marinas at arm.com> wrote:
>
> On Sat, Jul 31, 2021 at 01:01:25AM +0200, Andrey Konovalov wrote:
> > On Tue, Jul 27, 2021 at 8:54 PM Catalin Marinas <catalin.marinas at arm.com> wrote:
> > > On Wed, Jul 14, 2021 at 03:38:43PM +0100, Mark Rutland wrote:
> > > > We have special logic to suppress MTE tag check fault reporting, based
> > > > on a global `mte_report_once` and `reported` variables. These can be
> > > > used to suppress calling kasan_report() when taking a tag check fault,
> > > > but do not prevent taking the fault in the first place, nor does they
> > > > affect the way we disable tag checks upon taking a fault.
> > > >
> > > > The core KASAN code already defaults to reporting a single fault, and
> > > > has a `multi_shot` control to permit reporting multiple faults. The only
> > > > place we transiently alter `mte_report_once` is in lib/test_kasan.c,
> > > > where we also the `multi_shot` state as the same time. Thus
> > > > `mte_report_once` and `reported` are redundant, and can be removed.
> > > >
> > > > When a tag check fault is taken, tag checking will be disabled by
> > > > `do_tag_recovery` and must be explicitly re-enabled if desired. The test
> > > > code does this by calling kasan_enable_tagging_sync().
> > > >
> > > > This patch removes the redundant mte_report_once() logic and associated
> > > > variables.
> > >
> > > The first "reported" variable was added to avoid calling kasan_report on
> > > each CPU as we are lazily disabling tag checking when faults are
> > > triggered.
> >
> > So we do not need "reported" anymore? Why?
>
> Because kasan has its own mechanism with KASAN_BIT_REPORTED.

This mechanism only works when multi_shot is disabled. But milti_shot
is always enabled when running the tests. Yet I tested the series, and
I don't see multiple reports for each test, so everything somehow
works. But I don't understand how.