linux-kernel - Re: [RFC] Revert "kvm: nVMX: Restrict VMX capability MSR changes"

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Message-ID: <30525d58-10de-abb4-8dad-228da766ff82@redhat.com>
Date:   Mon, 20 Jan 2020 16:41:27 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [RFC] Revert "kvm: nVMX: Restrict VMX capability MSR changes"

On 20/01/20 16:11, Vitaly Kuznetsov wrote:
> 
> RFC. I think the check for vmx->nested.vmxon is legitimate for everything
> but restore so removing it (what I do with the revert) is likely a no-go.
> I'd like to gather opinions on the proper fix: should we somehow check
> that the vCPU is in 'restore' start (has never being run) and make
> KVM_SET_MSRS pass or should we actually mandate that KVM_SET_NESTED_STATE
> is run after KVM_SET_MSRS by userspace?
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>

I think this should be fixed in QEMU, by doing KVM_SET_MSRS for feature
MSRs way earlier.  I'll do it since I'm currently working on a patch to
add a KVM_SET_MSR for the microcode revision.

Thanks,

Paolo