Hi James, > -----Original Message----- > From: linux-arm-kernel <[email protected]> On > Behalf Of James Morse > Sent: Tuesday, February 26, 2019 2:29 AM > To: Zhang, Lei/張 雷 <[email protected]> > Cc: Mark Rutland <[email protected]>; 'Catalin Marinas' > <[email protected]>; 'Will Deacon' <[email protected]>; > '[email protected]' <[email protected]>; > '[email protected]' <[email protected]> > Subject: Re: [PATCH v4] arm64: Add workaround for Fujitsu A64FX erratum > 010001 > > 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<[email protected]> > > Thanks, I'll post it properly with this tag. [>] I saw v5 patch you posted. Thanks a lot.
> > > >> 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. [>] I agree with you (that there is no need to mention here). Thank you for your suggestion. Best Regards, Zhang Lei
