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From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v4 07/17] x86/split_lock: Enumerate #AC for split lock by
 MSR IA32_CORE_CAPABILITY
To:     Fenghua Yu <fenghua.yu@intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        x86 <x86@kernel.org>, kvm@vger.kernel.org
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Message-ID: <d582d469-40aa-287e-4368-723bf3ff4251@intel.com>
Date:   Mon, 4 Mar 2019 11:19:31 -0800
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On 3/4/19 10:59 AM, Fenghua Yu wrote:
>> 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?
> The function sets the split_lock_detect feature which needs to be
> applied before BSP calls apply_enforced_caps() in get_cpu_cap(). 

Why does it need to be applied that way?

> And I want to enable split lock detection in earlier phase to detect
> split lock earlier.

Why do you want to do this?  Why is this *required* as part of this
implementation?

... and how is this different than the other features that are processed
for cpus other than the boot CPU?