linux-kernel - Re: [PATCH v2 28/28] KVM: nVMX: Use cached host MSR_IA32_VMX

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Date:   Thu, 30 Jun 2022 09:36:39 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 28/28] KVM: nVMX: Use cached host MSR_IA32_VMX_MISC
 value for setting up nested MSR

Jim Mattson <jmattson@...gle.com> writes:

> On Wed, Jun 29, 2022 at 8:07 AM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>>
>> vmcs_config has cased host MSR_IA32_VMX_MISC value, use it for setting
>> up nested MSR_IA32_VMX_MISC in nested_vmx_setup_ctls_msrs() and avoid the
>> redundant rdmsr().
>>
>> No (real) functional change intended.
>
> Just imaginary functional change? :-)
>

Well, yea) The assumption here is that MSR_IA32_VMX_MISC's value doesn't
change underneath KVM, caching doesn't change anything then. It is, of
course, possible that when KVM runs as a nested hypervisor on top of
something else, it will observe different values. I truly hope this is
purely imaginary :-)

>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Reviewed-by: Jim Mattson <jmattson@...gle.com>
>

Thanks!

-- 
Vitaly