linux-kernel - Re: [PATCH v2 5/6] kvm: x86: Emulate MSR IA32_CORE

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Date:   Tue, 4 Feb 2020 10:37:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH v2 5/6] kvm: x86: Emulate MSR IA32_CORE_CAPABILITIES

On Tue, Feb 04, 2020 at 05:19:26PM +0800, Xiaoyao Li wrote:

> > > +	case MSR_IA32_CORE_CAPS:
> > > +		if (!msr_info->host_initiated)
> > 
> > Shouldn't @data be checked against kvm_get_core_capabilities()?
> 
> Maybe it's for the case that userspace might have the ability to emulate SLD
> feature? And we usually let userspace set whatever it wants, e.g.,
> ARCH_CAPABILITIES.

If the 'sq_misc.split_lock' event is sufficiently accurate, I suppose
the host could use that to emulate the feature at the cost of one
counter used.