linux-kernel - Re: [PATCH v5 3/9] x86/split_lock: Re-define the kernel param option for split_lock

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Date:   Wed, 25 Mar 2020 08:43:01 +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>,
        kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     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>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v5 3/9] x86/split_lock: Re-define the kernel param option
 for split_lock_detect

On 3/24/2020 6:40 PM, Thomas Gleixner wrote:
> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>> On 3/24/2020 1:10 AM, Thomas Gleixner wrote:
>>> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>>>
>>>> Change sld_off to sld_disable, which means disabling feature split lock
>>>> detection and it cannot be used in kernel nor can kvm expose it guest.
>>>> Of course, the X86_FEATURE_SPLIT_LOCK_DETECT is not set.
>>>>
>>>> Add a new optioin sld_kvm_only, which means kernel turns split lock
>>>> detection off, but kvm can expose it to guest.
>>>
>>> What's the point of this? If the host is not clean, then you better fix
>>> the host first before trying to expose it to guests.
>>
>> It's not about whether or not host is clean. It's for the cases that
>> users just don't want it enabled on host, to not break the applications
>> or drivers that do have split lock issue.
> 
> It's very much about whether the host is split lock clean.
> 
> If your host kernel is not, then this wants to be fixed first. If your
> host application is broken, then either fix it or use "warn".
> 

My thought is for CSPs that they might not turn on SLD on their product 
environment. Any split lock in kernel or drivers may break their service 
for tenants.