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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>
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <f6e76523-7727-6e79-7bcf-3d6c6ebd64d8@redhat.com>
Date:   Wed, 31 Jan 2018 16:42:58 -0500
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On 31/01/2018 16:05, Jim Mattson wrote:
> On Wed, Jan 31, 2018 at 1:00 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
>> Yes, but how would moving the field into struct loaded_vmcs do anything?
>>  Only vmon/vmoff would change anything in vmx->nested.vmcs02.
> 
> My suggestion was that nested_vmx_merge_msr_bitmap should set the
> vmcs02 version of save_spec_ctrl_on_exit based on the calculated value
> of the write permission bit for IA32_SPEC_CTRL in the vmcs02 MSR
> permission bitmap.
> 
>> 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?
> 
> Yes, it sucks to be L1 in this situation.

Can we just say it sucks to be L2 too? :)  Because in the end as long as
no one ever writes to spec_ctrl, everybody is happy.

Paolo