linux-kernel - Re: [PATCH v3 4/4] arm64: mte: Optimize mte_assign_mem_tag

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Message-ID: <0c1b9a6b-0326-a24f-6418-23a0723adecf@arm.com>
Date:   Sun, 17 Jan 2021 12:27:08 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Catalin Marinas <catalin.marinas@....com>,
        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>
Subject: Re: [PATCH v3 4/4] arm64: mte: Optimize mte_assign_mem_tag_range()

Hi Mark,

On 1/16/21 2:22 PM, Vincenzo Frascino wrote:
>> Is there any chance that this can be used for the last bytes of the
>> virtual address space? This might need to change to `_addr == _end` if
>> that is possible, otherwise it'll terminate early in that case.
>>
> Theoretically it is a possibility. I will change the condition and add a note
> for that.
> 

I was thinking to the end of the virtual address space scenario and I forgot
that if I use a condition like `_addr == _end` the tagging operation overflows
to the first granule of the next allocation. This disrupts tagging accesses for
that memory area hence I think that `_addr < _end` is the way to go.

-- 
Regards,
Vincenzo