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Subject: Re: [PATCH v5 4/5] KVM: VMX: Allow direct access to
 MSR_IA32_SPEC_CTRL
To:     Jim Mattson <jmattson@google.com>
Cc:     KarimAllah Ahmed <karahmed@amazon.com>,
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <16d89e09-fbfc-4a08-00a6-40cfb4776018@redhat.com>
Date:   Wed, 31 Jan 2018 16:00:43 -0500
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On 31/01/2018 15:54, Jim Mattson wrote:
> You seem to be making the assumption that there is one L2. What if
> there are 100 L2s, and only one has write-access to IA32_SPEC_CTRL? Or
> what if there once was such an L2, but it's been gone for months? The
> current mechanism penalizes *all* L2s if any L2, ever, has
> write-access to IA32_SPEC_CTRL.

Yes, but how would moving the field into struct loaded_vmcs do anything?
 Only vmon/vmoff would change anything in vmx->nested.vmcs02.

Even then, L1 vmexits will also be penalized because L1 has probably
done an RDMSR/WRMSR on L2->L1 vmexit.  So I don't think it's an issue?

Paolo