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: <87r1xidoj1.fsf@nanos.tec.linutronix.de>
Date:   Tue, 24 Mar 2020 11:40:18 +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 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".

Stop proliferating crap.

Thanks,

        tglx