Hi Zhang, On 23/02/2019 13:06, Zhang, Lei wrote: > Zhang, Lei wrote: >> I think you mean it may be a problem to modify the KPTI trampoline because >> some patches about KPTI will be merged to mainline in the near future. >> I understood that. >> I should discuss with my colleagues whether we can set NFDx=0 all of time on >> A64FX. > > The result of our investigation also supports your suggestion. > We surely agree with you that your proposed method (never set NFDx=1 on A64FX) > is the best to resolve this erratum. > > For this erratum, James's patch should be merged to mainline > instead of my previous patches (v1 to v4). > Since KPTI fully covers the effect of NFD1 for A64FX, KPTI is > recommended to be used in conjunction with James’s patch.
>> And thanks for your patch. >> If we can set NFDx=0 all of time, I will review, test and report the result. > > I have already tested James's patch on A64FX, and the result is no problem at > all. > > Tested-by:zhang.lei<zhang....@jp.fujitsu.com> Thanks, I'll post it properly with this tag. >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index >> a4168d366127..b0b7f1c4e816 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -643,6 +643,25 @@ config QCOM_FALKOR_ERRATUM_E1041 >> >> If unsure, say Y. >> >> +config FUJITSU_ERRATUM_010001 >> + bool "Fujitsu-A64FX erratum E#010001: Undefined fault may occur wrongly" >> + default y >> + help >> + This option adds workaround for Fujitsu-A64FX erratum E#010001. >> + On some variants of the Fujitsu-A64FX cores version (1.0, 1.1), memory >> + accesses may cause undefined fault (Data abort, DFSC=0b111111). >> + This fault occurs under a specific hardware condition when a >> + load/store instruction performs 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. >> + >> + The workaround is to ensure these bits are clear in TCR_ELx. >> + The workaround only affect the Fujitsu-A64FX. > > I think it is better to add a notice here as follows: > > Recommend to enable KPTI (UNMAP_KERNEL_AT_EL0 = y). That unmap option is on by default, you can't turn it off without CONFIG_EXPERT. While I agree, I don't think we need to spell this out. Thanks, James
