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

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Message-ID: <878sjpz1mr.fsf@nanos.tec.linutronix.de>
Date:   Wed, 25 Mar 2020 02:03:56 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xiaoyao Li <xiaoyao.li@...el.com>, 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

Xiaoyao Li <xiaoyao.li@...el.com> writes:

> 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.

Again you are proliferating crap and making excuses for Common Sense
violating Purposes (CSP).

Thanks,

        tglx