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 22:42:00 -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 10:25 AM, Paolo Bonzini wrote:
> 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.

The whole routine or just the bit checking?  I can see still needing the
check to be sure the "feature" is present.

Thanks,
Tom

> 
> Paolo
>