Re: [PATCH 1/5] KVM: nVMX: Fix VMX controls MSRs setup when nested VMX enabled

[Xiaoyao Li]

On 8/29/2020 9:49 AM, Chenyi Qiang wrote:
> On 8/29/2020 1:43 AM, Jim Mattson wrote:
> > On Fri, Aug 28, 2020 at 1:54 AM Chenyi Qiang <chenyi.qiang@xxxxxxxxx> 
> > wrote:
> > > KVM supports the nested VM_{EXIT, ENTRY}_LOAD_IA32_PERF_GLOBAL_CTRL and
> > > VM_{ENTRY_LOAD, EXIT_CLEAR}_BNDCFGS, but they doesn't expose during
> > > the setup of nested VMX controls MSR.
> >
> > Aren't these features added conditionally in
> > nested_vmx_entry_exit_ctls_update() and
> > nested_vmx_pmu_entry_exit_ctls_update()?
>
> Yes, but I assume vmcs_config.nested should reflect the global 
> capability of VMX MSR. KVM supports these two controls, so should be 
> exposed here.

No. I prefer to say they are removed conditionally in 
nested_vmx_entry_exit_ctls_update() and 
nested_vmx_pmu_entry_exit_ctls_update().

Userspace calls vmx_get_msr_feature() to query what KVM supports for 
these VMX MSR. In vmx_get_msr_feature(), it returns the value of 
vmcs_config.nested. As KVM supports these two bits, we should advertise 
them in vmcs_config.nested and report to userspace.