linux-kernel - Re: [PATCH v3 3/4] arm64: mte: Enable async tag check fault

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Message-ID: <ff8c61b3-1374-29c7-a4f3-9e37b61e5f3a@arm.com>
Date:   Mon, 18 Jan 2021 15:39:43 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Marco Elver <elver@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        Alexander Potapenko <glider@...gle.com>,
        linux-arm-kernel@...ts.infradead.org,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Will Deacon <will@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v3 3/4] arm64: mte: Enable async tag check fault



On 1/18/21 2:48 PM, Vincenzo Frascino wrote:
>> Are you aware of cases where the TFSR_EL1 value is read other than by an
>> MRS? e.g. are there any cases where checks are elided if TF1 is set? If
>> so, we may need the ISB to order the direct write against subsequent
>> indirect reads.
>>
> Thank you for the explanation. I am not aware of any case in which TFSR_EL1 is
> read other then by an MRS. Based on the ARM DDI 0487F.c (J1-7626) TF0/TF1 are
> always set to '1' without being accessed before. I will check with the
> architects for further clarification and if this is correct I will remove the
> isb() in the next version.
> 

I spoke to the architects and I confirm that the isb() can be removed.

-- 
Regards,
Vincenzo