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Subject: Re: [PATCH v12 6/7] arm64: mte: Save/Restore TFSR_EL1 during suspend
To:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Andrey Konovalov <andreyknvl@google.com>
References: <20210208165617.9977-1-vincenzo.frascino@arm.com>
 <20210208165617.9977-7-vincenzo.frascino@arm.com>
 <20210208185635.GA13187@e121166-lin.cambridge.arm.com>
From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <a6ac58ef-f437-8a77-d288-c4de3316692f@arm.com>
Date:   Tue, 9 Feb 2021 10:41:03 +0000
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Hi Lorenzo,

thank you for your review.

On 2/8/21 6:56 PM, Lorenzo Pieralisi wrote:
>>  u64 gcr_kernel_excl __ro_after_init;
>>  
>> +static u64 mte_suspend_tfsr_el1;
> IIUC you need this per-CPU (core loses context on suspend-to-RAM but also
> CPUidle, S2R is single threaded but CPUidle runs on every core idle
> thread).
> 
> Unless you sync/report it on enter/exit (please note: I am not familiar
> with MTE so it is just a, perhaps silly, suggestion to avoid
> saving/restoring it).
> 

I thought about making it per cpu, but I concluded that since it is an
asynchronous tag fault it wasn't necessary.

But thinking at it from the statistical point of view what you are saying is
completely right, because we might end up in scenario in which we report the
fault on multiple cores when it happens on one or in a scenario in which we do
not report the potential fault at all.

I am going to update my code accordingly in the next version.

Thanks!

> Lorenzo
> 

-- 
Regards,
Vincenzo