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    SubjectRe: [PATCH v2 1/6] arm64: cpufeature: Allow early detect of specific features
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    On 17/01/18 11:54, Julien Thierry wrote:
    > From: Daniel Thompson <daniel.thompson@linaro.org>
    >
    > Currently it is not possible to detect features of the boot CPU
    > until the other CPUs have been brought up.
    >
    > This prevents us from reacting to features of the boot CPU until
    > fairly late in the boot process. To solve this we allow a subset
    > of features (that are likely to be common to all clusters) to be
    > detected based on the boot CPU alone.
    >
    > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
    > [julien.thierry@arm.com: check non-boot cpu missing early features, avoid
    > duplicates between early features and normal
    > features]
    > Signed-off-by: Julien Thierry <julien.thierry@arm.com>
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Will Deacon <will.deacon@arm.com>
    > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
    > ---
    > arch/arm64/kernel/cpufeature.c | 69 ++++++++++++++++++++++++++++--------------
    > 1 file changed, 47 insertions(+), 22 deletions(-)
    >
    > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
    > index a73a592..6698404 100644
    > --- a/arch/arm64/kernel/cpufeature.c
    > +++ b/arch/arm64/kernel/cpufeature.c
    > @@ -52,6 +52,8 @@
    > DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
    > EXPORT_SYMBOL(cpu_hwcaps);
    >
    > +static void __init setup_early_feature_capabilities(void);
    > +
    > /*
    > * Flag to indicate if we have computed the system wide
    > * capabilities based on the boot time active CPUs. This
    > @@ -542,6 +544,8 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
    > init_cpu_ftr_reg(SYS_ZCR_EL1, info->reg_zcr);
    > sve_init_vq_map();
    > }
    > +
    > + setup_early_feature_capabilities();
    > }
    >
    > static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new)
    > @@ -846,7 +850,7 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus
    > ID_AA64PFR0_FP_SHIFT) < 0;
    > }
    >
    > -static const struct arm64_cpu_capabilities arm64_features[] = {
    > +static const struct arm64_cpu_capabilities arm64_early_features[] = {
    > {
    > .desc = "GIC system register CPU interface",
    > .capability = ARM64_HAS_SYSREG_GIC_CPUIF,
    > @@ -857,6 +861,10 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus
    > .sign = FTR_UNSIGNED,
    > .min_field_value = 1,
    > },
    > + {}
    > +};
    > +


    Julien,

    One potential problem with this is that we don't have a way
    to make this work on a "theoretical" system with and without
    GIC system reg interface. i.e, if we don't have the CONFIG
    enabled for using ICC system regs for IRQ flags, the kernel
    could still panic. I understand this is not a "normal" configuration
    but, may be we could make the panic option based on whether
    we actually use the system regs early enough ?

    Btw, I am rewriting the capabilities infrastructure to allow per-cap
    control on how it should be treated. I might add an EARLY scope for
    caps which could cover this and may be VHE.

    Suzuki

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