linux-kernel - Re: [PATCH v4 07/17] x86/split_lock: Enumerate #AC for split lock by MSR IA32_CORE

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Date:   Mon, 4 Mar 2019 10:58:01 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        kvm@...r.kernel.org
Subject: Re: [PATCH v4 07/17] x86/split_lock: Enumerate #AC for split lock by
 MSR IA32_CORE_CAPABILITY

>  	 * Clear/Set all flags overridden by options, after probe.
> diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
> index 2c0bd38a44ab..5ba11ce99f92 100644
> --- a/arch/x86/kernel/cpu/cpuid-deps.c
> +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> @@ -59,6 +59,7 @@ static const struct cpuid_dep cpuid_deps[] = {
>  	{ X86_FEATURE_AVX512_4VNNIW,	X86_FEATURE_AVX512F   },
>  	{ X86_FEATURE_AVX512_4FMAPS,	X86_FEATURE_AVX512F   },
>  	{ X86_FEATURE_AVX512_VPOPCNTDQ, X86_FEATURE_AVX512F   },
> +	{ X86_FEATURE_SPLIT_LOCK_DETECT, X86_FEATURE_CORE_CAPABILITY},
>  	{}
>  };

Please reindent the rest of the structure whenever you break the record
for name length.

> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index fc3c07fe7df5..0c44c49f6005 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1029,3 +1029,24 @@ static const struct cpu_dev intel_cpu_dev = {
>  
>  cpu_dev_register(intel_cpu_dev);
>  
> +/**
> + * init_core_capability - enumerate features supported in IA32_CORE_CAPABILITY
> + * @c: pointer to cpuinfo_x86
> + *
> + * Return: void
> + */
> +void init_core_capability(struct cpuinfo_x86 *c)
> +{
> +	/*
> +	 * If MSR_IA32_CORE_CAPABILITY exists, enumerate features that are
> +	 * reported in the MSR.
> +	 */
> +	if (c == &boot_cpu_data && cpu_has(c, X86_FEATURE_CORE_CAPABILITY)) {

First of all, please endeavor to leave the main flow of the function at
the first indent.

*If* you were to do this, it would look like:


	if (c != &boot_cpu_data)
		return;
	if (!cpu_has(c, X86_FEATURE_CORE_CAPABILITY))
		return;

	rdmsrl(...);

But, it goes unmentioned why you do the boot-cpu-only restriction here.
 It doesn't match the behavior of the two functions called before
init_core_capability():

        init_scattered_cpuid_features(c);
        init_speculation_control(c);

So why is this new function special?


> +		u64 val;
> +
> +		rdmsrl(MSR_IA32_CORE_CAPABILITY, val);
> +
> +		if (val & CORE_CAP_SPLIT_LOCK_DETECT)
> +			setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
> +	}
> +}
>