linux-kernel - Re: [PATCH v3 0/1] arm64: Add workaround for Fujitsu A64FX erratum 010001

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Date:   Wed, 30 Jan 2019 15:00:28 +0000
From:   James Morse <james.morse@....com>
To:     "Zhang, Lei" <zhang.lei@...fujitsu.com>
Cc:     'Catalin Marinas' <catalin.marinas@....com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        'Mark Rutland' <mark.rutland@....com>,
        "'linux-arm-kernel@...ts.infradead.org'" 
        <linux-arm-kernel@...ts.infradead.org>,
        "'will.deacon@....com'" <will.deacon@....com>
Subject: Re: [PATCH v3 0/1] arm64: Add workaround for Fujitsu A64FX erratum
 010001

Hi!

On 01/29/2019 12:29 PM, Zhang, Lei wrote:
> On some variants of the Fujitsu-A64FX cores ver(1.0, 1.1),
> memory accesses may cause undefined fault (Data abort, DFSC=0b111111).
> This problem will be fixed by next version of Fujitsu-A64FX.
> 
> This fault occurs under a specific hardware condition
> when a load/store instruction perform an address translation using:
>    case-1  TTBR0_EL1 with TCR_EL1.NFD0 == 1.
>    case-2  TTBR0_EL2 with TCR_EL2.NFD0 == 1.
>    case-3  TTBR1_EL1 with TCR_EL1.NFD1 == 1.
>    case-4  TTBR1_EL2 with TCR_EL2.NFD1 == 1.
> And this fault occurs completely spurious.
> 
> Since TCR_ELx.NFD1 is set to '1' at the kernel in versions
> past 4.17, the case-3 or case-4 may happen.

e03e61c3173c ("arm64: kaslr: Set TCR_EL1.NFD1 when 
CONFIG_RANDOMIZE_BASE=y") ?

So you'd never see it if you disabled CONFIG_RANDOMIZE_BASE?


Thanks,

James