linux-kernel - Re: [RFC PATCH 1/2] KVM: x86: Add a framework for supporting MSR-based features

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Date:   Tue, 13 Feb 2018 22:23:42 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [RFC PATCH 1/2] KVM: x86: Add a framework for supporting
 MSR-based features

On 2/13/2018 10:21 AM, Paolo Bonzini wrote:
> On 08/02/2018 23:58, Tom Lendacky wrote:
>> Provide a new KVM capability that allows bits within MSRs to be recognized
>> as features.  Two new ioctls are added to the VM ioctl routine to retrieve
>> the list of these MSRs and their values. The MSR features can optionally
>> be exposed based on a CPU and/or a CPU feature.
> 
> Yes, pretty much.  Just two changes:
> 
>> +struct kvm_msr_based_features {
>> +	u32 msr;			/* MSR to query */
>> +	u64 mask;			/* MSR mask */
>> +	const struct x86_cpu_id *match;	/* Match criteria */
>> +	u64 value;			/* MSR value */
> 
> 1) These two should be replaced by a kvm_x86_ops callback, because
> computing the value is sometimes a bit more complicated than just rdmsr
> (for example, MSRs for VMX capabilities depend on the kvm_intel.ko
> module parameters).

Ok, I'll rework this.

> 
> 
>> +	case KVM_CAP_GET_MSR_FEATURES:
> 
> This should be KVM_GET_MSR.

Yup, not sure what I was thinking there.

> 
>> +		r = msr_io(NULL, argp, do_get_msr_features, 1);
>> +		break;
> 
> 
> Bonus points for writing documentation :) and for moving the MSR> handling code to arch/x86/kvm/msr.{c,h}.

Yup, there will be documentation on it - I wanted to make sure the
direction was correct first.  Splitting out msr.c/msr.h might be
best as a separate patchset, let me see what's involved.

Thanks,
Tom

> 
> Thanks,
> 
> Paolo
>