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Subject: Re: [RFD] x86/split_lock: Request to Intel
To:     Thomas Gleixner <tglx@linutronix.de>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Radim Krcmar <rkrcmar@redhat.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        x86 <x86@kernel.org>, kvm@vger.kernel.org
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From:   Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <5da90713-9a0d-6466-64f7-db435ba07dbe@intel.com>
Date:   Fri, 18 Oct 2019 10:36:41 +0800
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On 10/17/2019 8:29 PM, Thomas Gleixner wrote:
> The more I look at this trainwreck, the less interested I am in merging any
> of this at all.
> 
> The fact that it took Intel more than a year to figure out that the MSR is
> per core and not per thread is yet another proof that this industry just
> works by pure chance.
> 

Whether it's per-core or per-thread doesn't affect much how we implement 
for host/native.

And also, no matter it's per-core or per-thread, we always can do 
something in VIRT.

Maybe what matters is below.

> Seriously, this makes only sense when it's by default enabled and not
> rendered useless by VIRT. Otherwise we never get any reports and none of
> the issues are going to be fixed.
>

For VIRT, it doesn't want old guest to be killed due to #AC. But for 
native, it doesn't want VIRT to disable the #AC detection

I think it's just about the default behavior that whether to disable the 
host's #AC detection or kill the guest (SIGBUS or something else) once 
there is an split-lock #AC in guest.

So we can provide CONFIG option to set the default behavior and module 
parameter to let KVM set/change the default behavior.