Messages in this thread | | | Date | Tue, 12 Jan 2021 11:50:14 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v3 09/21] arm64: cpufeature: Add global feature override facility |
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Hi Suzuki,
On 2021-01-12 09:17, Suzuki K Poulose wrote: > Hi Marc, > > On 1/11/21 7:48 PM, Marc Zyngier wrote:
[...]
>> diff --git a/arch/arm64/kernel/cpufeature.c >> b/arch/arm64/kernel/cpufeature.c >> index 894af60b9669..00d99e593b65 100644 >> --- a/arch/arm64/kernel/cpufeature.c >> +++ b/arch/arm64/kernel/cpufeature.c >> @@ -774,6 +774,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, >> u64 new) >> u64 strict_mask = ~0x0ULL; >> u64 user_mask = 0; >> u64 valid_mask = 0; >> + u64 override_val = 0, override_mask = 0; >> >> const struct arm64_ftr_bits *ftrp; >> struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg); >> @@ -781,9 +782,35 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, >> u64 new) >> if (!reg) >> return; >> >> + if (reg->override_mask && reg->override_val) { >> + override_mask = *reg->override_mask; >> + override_val = *reg->override_val; >> + } >> + >> for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) { >> u64 ftr_mask = arm64_ftr_mask(ftrp); >> s64 ftr_new = arm64_ftr_value(ftrp, new); >> + s64 ftr_ovr = arm64_ftr_value(ftrp, override_val); >> + >> + if ((ftr_mask & override_mask) == ftr_mask) { >> + if (ftr_ovr < ftr_new) { > > Here we assume that all the features are FTR_LOWER_SAFE. We could > probably use arm64_ftr_safe_value(ftrp, ftr_new, ftr_ovr) here ? > That would cover us for both HIGHER_SAFE and LOWER_SAFE features. > However that may be restrictive for FTR_EXACT, as we the safe > value would be set to "ftr->safe_val". I guess that may be better > than forcing to use an unsafe value for the boot CPU, which could > anyway conflict with the other CPUs and eventually trigger the > ftr alue to be safe_val.
I like the idea of using the helper, as it cleanups up the code a bit. However, not being to set a feature to a certain value could be restrictive, as in general, it means that we can only disable a feature and not adjust its level of support.
Take PMUVER for example: with the helper, I can't override it from v8.4 to v8.1. I can only go to v8.0.
Is it something we care about?
Thanks,
M. -- Jazz is not dead. It just smells funny...
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