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

From: James Morse
Date: Wed Jan 30 2019 - 10:00:35 EST


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