linux-kernel - Re: [PATCH 1/4] KVM: nVMX: support restore of VMX capability MSRs

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Date:   Mon, 28 Nov 2016 23:48:46 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 1/4] KVM: nVMX: support restore of VMX capability MSRs



On 28/11/2016 22:11, David Matlack wrote:
> > PINBASED_CTLS, PROCBASED_CTLS, EXIT_CTLS and ENTRY_CTLS can be derived
> > from their "true" counterparts, so I think it's better to remove the
> > "non-true" ones from struct nested_vmx (and/or add the "true" ones when
> > missing) and make them entirely computed.  But it can be done on top.
>
> Good point. And that would mean userspace does not need to restore the
> non-true MSRs, right?

Yes, sorry for being a bit too concise. :)

> KVM does not emulate MSR_IA32_VMX_BASIC[55]=0,
> and will probably never want to.

That's a separate question, MSR_IA32_VMX_BASIC[55]=0 basically means
that the "true" capabilities are the same as the "default" capabilities.
 If userspace wanted to set it that way, KVM right now would not hide
the "true" capability MSR, but on the other hand the nested hypervisor
should not even notice the difference.

Paolo