From mboxrd@z Thu Jan  1 00:00:00 1970
From: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH] arm64: mte: Clear SCTLR_EL1.TCF0 on exec
Date: Wed, 12 Feb 2020 17:03:50 +0000
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To: Peter Collingbourne <pcc@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>, Kostya Serebryany <kcc@google.com>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-arch@vger.kernel.org, Richard Earnshaw <Richard.Earnshaw@arm.com>, Szabolcs Nagy <szabolcs.nagy@arm.com>, Marc Zyngier <maz@kernel.org>, Kevin Brodsky <kevin.brodsky@arm.com>, linux-mm@kvack.org, Andrey Konovalov <andreyknvl@google.com>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Will Deacon <will@kernel.org>

On Thu, Dec 19, 2019 at 05:48:53PM -0800, Peter Collingbourne wrote:
> On Thu, Dec 19, 2019 at 12:32 PM Peter Collingbourne <pcc@google.com> wrote:
> > On Wed, Dec 11, 2019 at 10:45 AM Catalin Marinas
> > <catalin.marinas@arm.com> wrote:
> > > +       if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
> > > +               update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
> >
> > I don't entirely understand why yet, but I've found that this check is
> > insufficient for ensuring consistency between SCTLR_EL1.TCF0 and
> > sctlr_tcf0. In my Android test environment with some processes having
> > sctlr_tcf0=SCTLR_EL1_TCF0_SYNC and others having sctlr_tcf0=0, I am
> > seeing intermittent tag failures coming from the sctlr_tcf0=0
> > processes. With this patch:
[...]
> > Since sysreg_clear_set only sets the sysreg if it ended up changing, I
> > wouldn't expect this to cause a significant performance hit unless
> > just reading SCTLR_EL1 is expensive. That being said, if the
> > inconsistency is indicative of a deeper problem, we should probably
> > address that.
> 
> I tracked it down to the flush_mte_state() function setting sctlr_tcf0 but
> failing to update SCTLR_EL1.TCF0. With this patch I am not seeing any more
> inconsistencies.

Thanks Peter. I folded in your fix.

-- 
Catalin