Sean Christopherson <seanjc@xxxxxxxxxx> 于2023年3月11日周六 00:12写道：
>
> On Fri, Mar 10, 2023, Robert Hoo wrote:
> > Remove the unnecessary cpu_has_vmx_desc() check for emulating UMIP.
>
> It's not unnecessary. See commit 64f7a11586ab ("KVM: vmx: update sec exec controls
> for UMIP iff emulating UMIP"). Dropping the check will cause KVM to execute
>
> secondary_exec_controls_clearbit(vmx, SECONDARY_EXEC_DESC);
>
> on CPUs that don't have SECONDARY_VM_EXEC_CONTROL.
Sorry I don't follow you.
My point is that, given it has passed kvm_is_valid_cr4() (in
kvm_set_cr4()), we can assert
boot_cpu_has(X86_FEATURE_UMIP) and vmx_umip_emulated() must be at least one
true. Therefore when !boot_cpu_has(X86_FEATURE_UMIP),
vmx_umip_emulated() must be
true, therefore checking it is redundant.
Do you mean other call path other than kvm_set_cr4() --> vmx_set_cr4()? i.e.
vmx_set_cr0() --> vmx_set_cr4()?
nested_... --> vmx_set_cr4()?
Emm, they seem don't go through kvm_is_valid_cr4() firstly.
