Re: [PATCH] kvm: x86: remove vmx_vm_has_apicv() outside of hwapic_isr_update()

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/12/2014 03:32, Chen, Tiejun wrote:
> 
> Are you saying something below?
> 
> if (enable_apicv)
>     ...
> else {
>     kvm_x86_ops->hwapic_irr_update = NULL;

Yes.

> But this means we have to revise hadware_setup() to get 'kvm' inside,

This would not even be possible, since hardware_setup() is only called once.

However, for the only caller of hwapic_isr_update (but presumably all of
them, as is the case for hwapic_irr_update), you already know that
irqchip_in_kernel(kvm) is true.  You are in kvm_apic_post_state_restore,
which takes a kvm_lapic_state, and no lapic exists if
!irqchip_in_kernel(kvm).

(Yes, irqchip_in_kernel) is a bit weird and tests pic_irqchip(kvm)
instead, but it's the same.  It tests pic_irqchip(kvm) only because the
LAPIC is per-cpu and irqchip_in_kernel takes a struct kvm).

So it's possible to NULL out hwapic_isr_update in hardware_setup.  It
simply shouldn't happen that you call hwapic_isr_update without the
in-kernel irqchip.  The kernel knows nothing about ISR/IRR without the
in-kernel irqchip.

Paolo

> then rebase other callers to hwapic_isr_update(), is it really good?