linux-kernel - Re: [PATCH v6 4/8] kvm: x86: Emulate split-lock access as a write in emulator

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Message-ID: <afd05186-dd2d-5610-d03e-98f4ed93d15f@intel.com>
Date:   Wed, 25 Mar 2020 08:31:24 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v6 4/8] kvm: x86: Emulate split-lock access as a write in
 emulator

On 3/25/2020 8:00 AM, Thomas Gleixner wrote:
> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>>   
>> +bool split_lock_detect_on(void)
>> +{
>> +	return sld_state != sld_off;
>> +}
>> +EXPORT_SYMBOL_GPL(split_lock_detect_on);
> 
> 1) You export this function here
> 
> 2) You change that in one of the next patches to something else
> 
> 3) According to patch 1/8 X86_FEATURE_SPLIT_LOCK_DETECT is not set when
>     sld_state == sld_off. FYI, I did that on purpose.
> 
> AFAICT #1 and #2 are just historical leftovers of your previous patch
> series and the extra step was just adding more changed lines per patch
> for no value.
> 
> #3 changed the detection mechanism and at the same time the semantics of
> the feature flag.
> 
> So what's the point of this exercise?

Right. In this series, setting X86_FEATURE_SPLIT_LOCK_DETECT flag means 
SLD is turned on. Need to remove split_lock_detect_on(). Thanks for 
pointing out this.

> Thanks,
> 
>          tglx
>