Re: [Xen-devel] [RFC PATCH] x86/apicv: fix RTC periodic timer and apicv issue

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Xuquan (Euler) [mailto:xuquan8@xxxxxxxxxx]
> Sent: Monday, September 12, 2016 5:08 PM
> 
> On September 12, 2016 3:58 PM, Tian, Kevin <kevin.tian@xxxxxxxxx> wrote:
> >> From: Xuquan (Euler) [mailto:xuquan8@xxxxxxxxxx]
> >> Sent: Friday, September 09, 2016 11:02 AM
> >>
> >> On August 30, 2016 1:58 PM, Tian Kevin < kevin.tian@xxxxxxxxx > wrote:
> >> >> From: Xuquan (Euler) [mailto:xuquan8@xxxxxxxxxx]
> >> >> Sent: Friday, August 19, 2016 8:59 PM
> >> diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
> >> index 1d5d287..cc247c3 100644
> >> --- a/xen/arch/x86/hvm/vlapic.c
> >> +++ b/xen/arch/x86/hvm/vlapic.c
> >> @@ -433,6 +433,11 @@ void vlapic_EOI_set(struct vlapic *vlapic)  void
> >> vlapic_handle_EOI(struct vlapic *vlapic, u8 vector)  {
> >>      struct domain *d = vlapic_domain(vlapic);
> >> +    struct hvm_intack pt_intack;
> >> +
> >> +    pt_intack.vector = vector;
> >> +    pt_intack.source = hvm_intsrc_lapic;
> >> +    pt_intr_post(vlapic_vcpu(vlapic), pt_intack);
> >>
> >>      if ( vlapic_test_and_clear_vector(vector,
> >&vlapic->regs->data[APIC_TMR]) )
> >>          vioapic_update_EOI(d, vector); diff --git
> >> a/xen/arch/x86/hvm/vmx/intr.c b/xen/arch/x86/hvm/vmx/intr.c index
> >> 8fca08c..29d9bbf 100644
> >> --- a/xen/arch/x86/hvm/vmx/intr.c
> >> +++ b/xen/arch/x86/hvm/vmx/intr.c
> >> @@ -333,8 +333,6 @@ void vmx_intr_assist(void)
> >>              clear_bit(i, &v->arch.hvm_vmx.eoi_exitmap_changed);
> >>              __vmwrite(EOI_EXIT_BITMAP(i),
> >v->arch.hvm_vmx.eoi_exit_bitmap[i]);
> >>          }
> >> -
> >> -        pt_intr_post(v, intack);
> >>      }
> >>      else
> >>      {
> >>
> >
> >Because we update pt irq in every vmentry, there is a chance that
> >already-injected instance (before EOI-induced exit happens) will incur 
> >another
> >pending IRR setting if there is a VM-exit happens between HW virtual 
> >interrupt
> >injection (vIRR->0, vISR->1) and EOI-induced exit (vISR->0), since 
> >pt_intr_post
> >hasn't been invoked yet. I guess this is the reason why you still see faster
> >wallclock.
> >
> 
> Agreed. A good description. My bad description is from another aspect.
> 
> >I think you need mark this pending_intr_post situation explicitly.
> >Then pt_update_irq should skip such pt timer when pending_intr_post of that
> >timer is true (otherwise the update is meaningless since previous one hasn't
> >been posted yet). Then with your change to post in EOI-induced exit handler, 
> >it
> >should work correctly to meet the goal
> >- one virtual interrupt delivery for one pending pt intr...
> >
> I think we are at least on the right track.
> But I can't follow ' pending_intr_post ', a new parameter? Thanks.
> 
> 

yes, a new parameter to record whether a intr_post operation is pending

Thanks
Kevin

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