linux-kernel - Re: [PATCH 2/3] x86/split_lock: Bits in IA32_CORE

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Message-ID: <20200418043534.GG15609@linux.intel.com>
Date:   Fri, 17 Apr 2020 21:35:35 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Luck, Tony" <tony.luck@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 2/3] x86/split_lock: Bits in IA32_CORE_CAPABILITIES are
 not architectural

On Sat, Apr 18, 2020 at 12:15:57PM +0800, Xiaoyao Li wrote:
> So now, it's tightly associated with CPU model, which makes it harder to
> expose this feature to guest. For guest, the CPU model can be configured to
> anything.
> 
> As suggested by Sean internally, we'd better use a KVM CPUID to expose it to
> guest, which makes it independent of CPU model.

Making this a paravirt feature from a KVM perspective would also let us do
the whole STICKY bit thing straight away.  I don't like paravirtualizing
something that could be emulated as-is, I but dislike it less than exposing
features based on CPU model.