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

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Message-ID: <87wo6dxhxf.fsf@nanos.tec.linutronix.de>
Date:   Sat, 18 Apr 2020 11:27:24 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        "Luck\, Tony" <tony.luck@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     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>,
        Sean Christopherson <sean.j.christopherson@...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

Xiaoyao,

can you please trim your replies?

Xiaoyao Li <xiaoyao.li@...el.com> writes:
> On 4/18/2020 5:07 AM, Thomas Gleixner wrote:
>> + * Bits in the IA32_CORE_CAPABILITIES are not architectural, so they should
>> + * only be trusted if it is confirmed that a CPU model implements a
>> + * specific feature at a particular bit position.
>> + *
>> + * The possible driver data field values:
>> + *
>> + * - 0: CPU models that are known to have the per-core split-lock detection
>> + *	feature even though they do not enumerate IA32_CORE_CAPABILITIES.
>> + *
>> + * - 1: CPU models which may enumerate IA32_CORE_CAPABILITIES and if so use
>> + *      bit 5 to enumerate the per-core split-lock detection feature.
>
> 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.

Works for me.

Thanks,

        tglx