Re: [PATCH v5 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL

[Jim Mattson]

On Wed, Jan 31, 2018 at 1:00 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> 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.