linux-kernel - Re: [PATCH v9 8/8] x86/split_lock: Enable split lock detection initialization when running as an guest on KVM

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Date:   Mon, 11 May 2020 09:11:20 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v9 8/8] x86/split_lock: Enable split lock detection
 initialization when running as an guest on KVM

On 5/10/2020 1:15 PM, Andy Lutomirski wrote:
> On Fri, May 8, 2020 at 8:04 PM Xiaoyao Li <xiaoyao.li@...el.com> wrote:
>>
>> When running as guest, enumerating feature split lock detection through
>> CPU model is not easy since CPU model is configurable by host VMM.
>>
>> If running upon KVM, it can be enumerated through
>> KVM_FEATURE_SPLIT_LOCK_DETECT,
> 
> This needs crystal clear documentation.  What, exactly, is the host
> telling the guest if it sets this flag?
> 
>> and if KVM_HINTS_SLD_FATAL is set, it
>> needs to be set to sld_fatal mode.
> 
> 
> This needs much better docs.  Do you mean:
> 
> "If KVM_HINTS_SLD_FATAL is set, then the guest will get #AC if it does
> a split-lock regardless of what is written to MSR_TEST_CTRL?"
> 

Hi Andy,

KVM_FEATURE_SPLIT_LOCK_DETECT, KVM_HINTS_SLD_FATAL and their docs are 
introduced in Patch 5. Do I still need to explain them in detail in this 
patch?