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linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 28-04-2025 21:05, MikoĊ‚aj Lenczewski wrote: > +config ARM64_BBML2_NOABORT > + bool "Enable support for Break-Before-Make Level 2 detection and usage" > + default y > + help > + FEAT_BBM provides detection of support levels for break-before-make > + sequences. If BBM level 2 is supported, some TLB maintenance requirements > + can be relaxed to improve performance. We additonally require the typo additonally -> additionally > + 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. > + > + To enable detection of BBML2 support, and to make use of it, say Y. > + > + Detection of and support for BBM level 2 can optionally be overridden > + at runtime via the use of the arm64.nobbml2 kernel commandline > + parameter. If your system claims support for BBML2, but is unstable > + with this option enabled, either say N or make use of the commandline > + parameter override to force BBML0. > + > endmenu # "ARMv8.4 architectural features" > [clip] > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 9c4d6d552b25..7a85a1bdc6e9 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -2200,6 +2200,70 @@ static bool hvhe_possible(const struct arm64_cpu_capabilities *entry, > return arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_HVHE); > } > > +static bool cpu_has_bbml2_noabort(unsigned int cpu_midr) > +{ > + /* > + * We want to allow usage of bbml2 in as wide a range of kernel contexts > + * as possible. This list is therefore an allow-list of known-good > + * implementations that both support bbml2 and additionally, fulfill the > + * extra constraint of never generating TLB conflict aborts when using > + * the relaxed bbml2 semantics (such aborts make use of bbml2 in certain > + * kernel contexts difficult to prove safe against recursive aborts). > + * > + * Note that implementations can only be considered "known-good" if their > + * implementors attest to the fact that the implementation never raises > + * TLBI conflict aborts for bbml2 mapping granularity changes. > + */ use bbml2 -> BBML2 to maintain consistency > + static const struct midr_range supports_bbml2_noabort_list[] = { > + MIDR_REV_RANGE(MIDR_CORTEX_X4, 0, 3, 0xf), > + MIDR_REV_RANGE(MIDR_NEOVERSE_V3, 0, 2, 0xf), > + {} > + }; > + > + return is_midr_in_range_list(cpu_midr, supports_bbml2_noabort_list); > +} > + > +static inline unsigned int cpu_read_midr(int cpu) > +{ > + WARN_ON_ONCE(!cpu_online(cpu)); > + > + return per_cpu(cpu_data, cpu).reg_midr; > +} > + Thanks Alok