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

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Message-ID: <45f3c26d-9580-7336-6c74-a0c1cd1e8963@redhat.com>
Date:   Tue, 13 Feb 2018 17:21:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....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 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).


> +	case KVM_CAP_GET_MSR_FEATURES:

This should be KVM_GET_MSR.

> +		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}.

Thanks,

Paolo