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

[KarimAllah Ahmed <karahmed@amazon.com>]

On 01/31/2018 08:53 PM, Jim Mattson wrote:
> On Wed, Jan 31, 2018 at 11:37 AM, KarimAllah Ahmed <karahmed@amazon.de> wrote:
> 
>> +
>> +       if (to_vmx(vcpu)->save_spec_ctrl_on_exit) {
>> +               nested_vmx_disable_intercept_for_msr(
>> +                               msr_bitmap_l1, msr_bitmap_l0,
>> +                               MSR_IA32_SPEC_CTRL,
>> +                               MSR_TYPE_R | MSR_TYPE_W);
>> +       }
>> +
> 
> As this is written, L2 will never get direct access to this MSR until
> after L1 writes it.  What if L1 never writes it? The condition should
> really be something that captures, "if L0 is willing to yield this MSR
> to the guest..."

but save_spec_ctrl_on_exit is also set for L2 write. So once L2 writes
to it, this condition will be true and then the bitmap will be updated.

> 
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