linux-kernel - Re: [PATCH v12 6/7] arm64: mte: Save/Restore TFSR

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Date:   Tue, 9 Feb 2021 11:55:33 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v12 6/7] arm64: mte: Save/Restore TFSR_EL1 during suspend

On Mon, Feb 08, 2021 at 04:56:16PM +0000, Vincenzo Frascino wrote:
> When MTE async mode is enabled TFSR_EL1 contains the accumulative
> asynchronous tag check faults for EL1 and EL0.
> 
> During the suspend/resume operations the firmware might perform some
> operations that could change the state of the register resulting in
> a spurious tag check fault report.
> 
> Save/restore the state of the TFSR_EL1 register during the
> suspend/resume operations to prevent this to happen.

Do we need a similar fix for TFSRE0_EL1? We get away with this if
suspend is only entered on the idle (kernel) thread but I recall we
could also enter suspend on behalf of a user process (I may be wrong
though).

If that's the case, it would make more sense to store the TFSR* regs in
the thread_struct alongside sctlr_tcf0. If we did that, we'd not need
the per-cpu mte_suspend_tfsr_el1 variable.

-- 
Catalin