linux-kernel - Re: [PATCH v13 4/7] arm64: mte: Enable TCO in functions that can read beyond buffer limits

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Message-ID: <6865788c-7e63-fbd7-bb88-ba01eafb2f63@arm.com>
Date:   Tue, 23 Feb 2021 12:22:27 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....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 v13 4/7] arm64: mte: Enable TCO in functions that can read
 beyond buffer limits


On 2/23/21 12:05 PM, Catalin Marinas wrote:
>> I totally agree on this point. In the case of runtime switching we might need
>> the rethink completely the strategy and depends a lot on what we want to allow
>> and what not. For the kernel I imagine we will need to expose something in sysfs
>> that affects all the cores and then maybe stop_machine() to propagate it to all
>> the cores. Do you think having some of the cores running in sync mode and some
>> in async is a viable solution?
> stop_machine() is an option indeed. I think it's still possible to run
> some cores in async while others in sync but the static key here would
> only be toggled when no async CPUs are left.
> 

In such a case we might need to track the state based on cpuid() and have a mask
that tells us when cpus are all sync.
Not as expensive as stop_machine() but still requires a valid use case to be
introduced according to me.

-- 
Regards,
Vincenzo