Re: [PATCH 6/6] KVM: VMX: enable IPI virtualization

[Zeng Guang]

On 7/19/2021 4:32 AM, Paolo Bonzini wrote:
> On 17/07/21 05:55, Zeng Guang wrote:
> > > > +    if (vmx->ipiv_active)
> > > > +        install_pid(vmx);
> > > This should be if (enable_ipiv) instead, I think.
> > >
> > > In fact, in all other places that are using vmx->ipiv_active, you can
> > > actually replace it with enable_ipiv; they are all reached only with
> > > kvm_vcpu_apicv_active(vcpu) == true.
> > enable_ipiv as a global variable indicates the hardware capability to
> > enable IPIv. Each VM may have different IPIv configuration according to
> > kvm_vcpu_apicv_active status. So we use ipiv_active per VM to enclose
> > IPIv related operations.
> Understood, but in practice all uses of vmx->ipiv_active are guarded by
> kvm_vcpu_apicv_active so they are always reached with vmx->ipiv_active
> == enable_ipiv.
>
> The one above instead seems wrong and should just use enable_ipiv.
enable_ipiv associate with "IPI virtualization" setting in tertiary exec 
controls and
enable_apicv which depends on cpu_has_vmx_apicv(). kvm_vcpu_apicv_active 
still
can be false even if enable_ipiv is true, e.g. in case irqchip not 
emulated in kernel.

Though it's ok to use enable_ipiv here, vmcs setup succeed for IPIv but 
it won't take into effect as
false kvm_vcpu_apicv_active runtime disable “IPI virtualization" for VM 
in this case and
leads vmx->ipiv_active become false as well. So vmx->ipiv_active is more 
accurate to reflect
runtime IPIv status.
> Paolo