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

From: Catalin Marinas <catalin.marinas@arm.com>
To: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Alexander Potapenko <glider@google.com>,
	Peter Collingbourne <pcc@google.com>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH 3/3] arm64: kasan: mte: remove redundant mte_report_once logic
Date: Sat, 31 Jul 2021 03:44:32 -0700	[thread overview]
Message-ID: <20210731104430.GA1112@arm.com> (raw)
In-Reply-To: <CA+fCnZcLE=DcVcq1TfLxRSOnBfD-iy2iGgyxg7zHk28YxWTHbQ@mail.gmail.com>

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@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.

-- 
Catalin

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