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

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2014/12/19 19:12, Paolo Bonzini wrote:
>
>
> 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.

Yeah.

>
> 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

There are two other callers to hwapic_isr_update(), apic_set_isr() and 
apic_clear_isr(), but I think they still work here.

> 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.

Thanks for your kind elaboration which always benefits me.

What about this revision as follows?

  kvm: x86: vmx: NULL out hwapic_isr_update() in case of !enable_apicv

In most cases calling hwapic_isr_update(), we always check if
kvm_apic_vid_enabled() == 1, but actually,
kvm_apic_vid_enabled()
     -> kvm_x86_ops->vm_has_apicv()
         -> vmx_vm_has_apicv() or '0' in svm case
             -> return enable_apicv && irqchip_in_kernel(kvm)

So its a little cost to recall vmx_vm_has_apicv() inside
hwapic_isr_update(), here just NULL out hwapic_isr_update() in
case of !enable_apicv inside hardware_setup() then make all
related stuffs follow this. Note we don't check this under that
condition of irqchip_in_kernel() since we should make sure
definitely any caller don't work  without in-kernel irqchip.

Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
---
  arch/x86/kvm/lapic.c | 7 ++++---
  arch/x86/kvm/vmx.c   | 4 +---
  2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 4f0c0b9..eb4cd5e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -402,7 +402,7 @@ static inline void apic_set_isr(int vec, struct 
kvm_lapic *apic)
          * because the processor can modify ISR under the hood.  Instead
          * just set SVI.
          */
-       if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
+       if (unlikely(kvm_x86_ops->hwapic_isr_update))
                 kvm_x86_ops->hwapic_isr_update(vcpu->kvm, vec);
         else {
                 ++apic->isr_count;
@@ -450,7 +450,7 @@ static inline void apic_clear_isr(int vec, struct 
kvm_lapic *apic)
          * on the other hand isr_count and highest_isr_cache are unused
          * and must be left alone.
          */
-       if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
+       if (unlikely(kvm_x86_ops->hwapic_isr_update))
                 kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
 
apic_find_highest_isr(apic));
         else {
@@ -1742,7 +1742,8 @@ void kvm_apic_post_state_restore(struct kvm_vcpu 
*vcpu,
         if (kvm_x86_ops->hwapic_irr_update)
                 kvm_x86_ops->hwapic_irr_update(vcpu,
                                 apic_find_highest_irr(apic));
-       kvm_x86_ops->hwapic_isr_update(vcpu->kvm, 
apic_find_highest_isr(apic));
+       if (kvm_x86_ops->hwapic_isr_update)
+           kvm_x86_ops->hwapic_isr_update(vcpu->kvm, 
apic_find_highest_isr(apic));
         kvm_make_request(KVM_REQ_EVENT, vcpu);
         kvm_rtc_eoi_tracking_restore_one(vcpu);
  }
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 96c84a8..e378dff 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5895,6 +5895,7 @@ static __init int hardware_setup(void)
                 kvm_x86_ops->update_cr8_intercept = NULL;
         else {
                 kvm_x86_ops->hwapic_irr_update = NULL;
+               kvm_x86_ops->hwapic_isr_update = NULL;
                 kvm_x86_ops->deliver_posted_interrupt = NULL;
                 kvm_x86_ops->sync_pir_to_irr = vmx_sync_pir_to_irr_dummy;
         }
@@ -7471,9 +7472,6 @@ static void vmx_hwapic_isr_update(struct kvm *kvm, 
int isr)
         u16 status;
         u8 old;

-       if (!vmx_vm_has_apicv(kvm))
-               return;
-
         if (isr == -1)
                 isr = 0;

-- 
1.9.1

I can send out as a patch if we have on any objections.

Thanks
Tiejun