linux-kernel - Re: [PATCH 2/2] arm64: Use static keys for CPU features

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Date:   Fri, 2 Sep 2016 16:52:25 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: Use static keys for CPU features

On Fri, Aug 26, 2016 at 10:22:13AM +0100, Suzuki K. Poulose wrote:
> On 25/08/16 18:26, Catalin Marinas wrote:
> > static inline int __attribute_const__
> >diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> >index 62272eac1352..919b2d0d68ae 100644
> >--- a/arch/arm64/kernel/cpufeature.c
> >+++ b/arch/arm64/kernel/cpufeature.c
> >@@ -46,6 +46,9 @@ unsigned int compat_elf_hwcap2 __read_mostly;
> >
> > DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
> >
> >+DEFINE_STATIC_KEY_ARRAY_FALSE(cpu_hwcap_keys, ARM64_NCAPS);
> >+EXPORT_SYMBOL(cpu_hwcap_keys);
> >+
> > #define __ARM64_FTR_BITS(SIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
> > 	{						\
> > 		.sign = SIGNED,				\
> >diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> >index ed1b84fe6925..6a141e399daf 100644
> >--- a/arch/arm64/kernel/cpuinfo.c
> >+++ b/arch/arm64/kernel/cpuinfo.c
> >@@ -377,6 +377,12 @@ void cpuinfo_store_cpu(void)
> > void __init cpuinfo_store_boot_cpu(void)
> > {
> > 	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, 0);
> >+
> >+	/*
> >+	 * Initialise the static keys early as they may be enabled by
> >+	 * check_local_cpu_errata() -> update_cpu_capabilities().
> >+	 */
> >+	jump_label_init();
> > 	__cpuinfo_store_cpu(info);
> 
> Just a heads up. I have a patch [1] which moves the "check_local_cpu_errata()"
> around to smp_prepare_boot_cpu(). This patch should still work fine with that
> case. Only that may be we could move the jump_lable_init() to smp_prepare_boot_cpu(),
> before we call "update_cpu_errata_work_arounds()" for Boot CPU.

IIUC, we wouldn't call update_cpu_errata_work_arounds() until the CPU
feature infrastructure is initialised via cpuinfo_store_boot_cpu(). So
I don't think moving the jump_label_init() call above is necessary.

> [1] https://lkml.kernel.org/r/1471525832-21209-4-git-send-email-suzuki.poulose@arm.com

-- 
Catalin