linux-kernel - Re: [PATCH v4 24/25] KVM: VMX: Cache MSR_IA32_VMX_MISC in vmcs

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Date:   Tue, 2 Aug 2022 16:28:14 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 24/25] KVM: VMX: Cache MSR_IA32_VMX_MISC in vmcs_config

On Tue, Aug 02, 2022, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@...gle.com> writes:
> 
> > On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> >> @@ -2613,6 +2614,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> >>  	if (((vmx_msr_high >> 18) & 15) != 6)
> >>  		return -EIO;
> >>  
> >> +	rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
> >
> > Might make sense to sanitize fields that KVM doesn't use and that are not exposed
> > to L1.  Not sure it's worthwhile though as many of the bits fall into a grey area,
> > e.g. all the SMM stuff isn't technically used by KVM, but that's largely because
> > much of it just isn't relevant to virtualization.
> >
> > I'm totally ok leaving it as-is, though maybe name it "unsanitized_misc" or so
> > to make that obvious?
> 
> I couldn't convince myself to add 'unsanitized_' prefix as I don't think
> it significantly reduces possible confusion (the quiestion would be
> 'sanitized for what and in which way?') so a need for 'git grep' seems
> imminent anyway.

Yeah, no objection to leaving it alone.  VMX_MISC is such an oddball MSR that it
practically comes with disclaimers anyways :-)