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If BBM level 2 is supported, some TLB maintenance >>>> requirements >>>> +      can be relaxed to improve performance. We additonally require the >>>> +      property that the implementation cannot ever raise TLB >>>> Conflict Aborts. >>>> +      Selecting N causes the kernel to fallback to BBM level 0 >>>> behaviour >>>> +      even if the system supports BBM level 2. >>>> + >>>>   endmenu # "ARMv8.4 architectural features" >>>>     menu "ARMv8.5 architectural features" >>>> diff --git a/arch/arm64/include/asm/cpucaps.h >>>> b/arch/arm64/include/asm/cpucaps.h >>>> index 0b5ca6e0eb09..2d6db33d4e45 100644 >>>> --- a/arch/arm64/include/asm/cpucaps.h >>>> +++ b/arch/arm64/include/asm/cpucaps.h >>>> @@ -23,6 +23,8 @@ cpucap_is_possible(const unsigned int cap) >>>>           return IS_ENABLED(CONFIG_ARM64_PAN); >>>>       case ARM64_HAS_EPAN: >>>>           return IS_ENABLED(CONFIG_ARM64_EPAN); >>>> +    case ARM64_HAS_BBML2_NOABORT: >>>> +        return IS_ENABLED(CONFIG_ARM64_BBML2_NOABORT); >>>>       case ARM64_SVE: >>>>           return IS_ENABLED(CONFIG_ARM64_SVE); >>>>       case ARM64_SME: >>>> diff --git a/arch/arm64/include/asm/cpufeature.h >>>> b/arch/arm64/include/asm/cpufeature.h >>>> index e0e4478f5fb5..108ef3fbbc00 100644 >>>> --- a/arch/arm64/include/asm/cpufeature.h >>>> +++ b/arch/arm64/include/asm/cpufeature.h >>>> @@ -866,6 +866,11 @@ static __always_inline bool >>>> system_supports_mpam_hcr(void) >>>>       return alternative_has_cap_unlikely(ARM64_MPAM_HCR); >>>>   } >>>>   +static inline bool system_supports_bbml2_noabort(void) >>>> +{ >>>> +    return alternative_has_cap_unlikely(ARM64_HAS_BBML2_NOABORT); >>>> +} >>> Hi Miko, >>> >>> I added AmpereOne mdir on top of this patch. I can see BBML2 feature is >>> detected via dmesg. But system_supports_bbml2_noabort() returns false. >>> The warning in the below debug patch is triggered: >>> >>> diff --git a/arch/arm64/kernel/cpufeature.c >>> b/arch/arm64/kernel/cpufeature.c >>> index faa9094d97dd..a70829ae2bd0 100644 >>> --- a/arch/arm64/kernel/cpufeature.c >>> +++ b/arch/arm64/kernel/cpufeature.c >>> @@ -3814,6 +3814,9 @@ void __init setup_system_features(void) >>>  { >>>         setup_system_capabilities(); >>> >>> +       if (!system_supports_bbml2_noabort()) >>> +               WARN_ON_ONCE(1); >>> + >>>         kpti_install_ng_mappings(); >>> >>>         sve_setup(); >>> >>> I thought it may be too early. But it seems other system features work >>> well, for example, MPAM. I didn't figure out why. It is weird. >> I just figured out the problem It is because the wrong kconfig name is used >> in cpucaps.h. The code is: >> >> +    case ARM64_HAS_BBML2_NOABORT: >> +        return IS_ENABLED(CONFIG_ARM64_BBML2_NOABORT); >> >> But the kconfig name actually is: >> >> +config ARM64_ENABLE_BBML2_NOABORT >> >> IMHO, the "ENABLE" in kconfig name sounds unnecessary. >> >> Thanks, >> Yang >> >> > Hi Yang, > > Thank you for the review, and apologies for the slight delay. > > Thanks again for the spot, I agree that `ENABLE` is probably redundant > (and clearly, caused an issue here). Will remove this. Please let me > know if there are any other issues with rebasing your patches on top of > mine. Thank you. I didn't spot any other problem on our machines. With this addressed, you can have Tested-by: Yang Shi , although I can't test on asymmetric system. Yang >