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

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Message-ID: <1105042a-327b-9be9-c0be-5f07f7110852@redhat.com>
Date:   Tue, 13 Feb 2018 17:25:32 +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:
> +bool kvm_valid_msr_feature(u32 msr, u64 data)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < num_msr_based_features; i++) {
> +		struct kvm_msr_based_features *m = msr_based_features + i;
> +
> +		if (msr != m->msr)
> +			continue;
> +
> +		/* Make sure not trying to change unsupported bits */
> +		return (data & ~m->mask) ? false : true;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(kvm_valid_msr_feature);
> +

This is probably unnecessary too (the allowed values are a bit more
complicated for, you just guessed it, VMX capability MSRs) and you can
just check bits other than LFENCE in svm_set_msr.

Paolo