linux-kernel - Re: [patch v2 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect

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Date:   Thu, 02 Apr 2020 19:34:35 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Kenneth R. Crudup" <kenny@...ix.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Nadav Amit <namit@...are.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch v2 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect

Xiaoyao Li <xiaoyao.li@...el.com> writes:
> On 4/3/2020 12:25 AM, Peter Zijlstra wrote:
>> On Fri, Apr 03, 2020 at 12:20:08AM +0800, Xiaoyao Li wrote:
>>> And, shouldn't we clear X86_FEATURE_SPLIT_LOCK_DETECT flag?
>> 
>> Don't think you can do that this late. Also, the hardware has the MSR
>> and it works, it's just that we should not.
>> 
>
> Actually, I agree to keep this flag.
>
> But, during the previous patch review, tglx wants to make
>
> 	sld_off = no X86_FEATURE_SPLIT_LOCK_DETECT
>
> I'm not sure whether he still insists on it now.

Obviously I cant.

> I really want to decouple sld_off and X86_FEATURE_SPLIT_LOCK_DETECT.
> So if X86_FEATURE_SPLIT_LOCK_DETECT is set, we can virtualize and expose 
> it to guest even when host is sld_off.

Can we first have a sane solution for the problem at hand?

Aside of that I'm still against the attempt of proliferating crap,
i.e. disabling it because the host is triggering it and then exposing it
to guests. The above does not change my mind in any way. This proposal
is still wrong.

Thanks,

        tglx