Re: [Xen-devel] [PATCH v6 15/18] vmx: Properly handle notification event when vCPU is running

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Monday, September 07, 2015 8:10 PM
> To: Wu, Feng; Zhang, Yang Z
> Cc: Andrew Cooper; Tian, Kevin; xen-devel@xxxxxxxxxxxxx; Keir Fraser
> Subject: Re: [PATCH v6 15/18] vmx: Properly handle notification event when
> vCPU is running
> 
> >>> On 25.08.15 at 03:57, <feng.wu@xxxxxxxxx> wrote:
> > --- a/xen/arch/x86/hvm/vmx/vmx.c
> > +++ b/xen/arch/x86/hvm/vmx/vmx.c
> >  const struct hvm_function_table * __init start_vmx(void)
> >  {
> >      set_in_cr4(X86_CR4_VMXE);
> > @@ -2073,7 +2119,7 @@ const struct hvm_function_table * __init
> start_vmx(void)
> >
> >      if ( cpu_has_vmx_posted_intr_processing )
> >      {
> > -        alloc_direct_apic_vector(&posted_intr_vector,
> event_check_interrupt);
> > +        alloc_direct_apic_vector(&posted_intr_vector,
> pi_notification_interrupt);
> >
> >          if ( iommu_intpost )
> >              alloc_direct_apic_vector(&pi_wakeup_vector,
> pi_wakeup_interrupt);
> 
> Considering that you do this setup independent of iommu_intpost,
> won't this (namely, but not only) for the !iommu_inpost case result
> in a whole lot of useless softirqs to be raised? 

I don't think lots of useless softirqs will be raised in !iommu_intpost
case, since we can get pi_notification_interrupt() only when someone
called __vmx_deliver_posted_interrupt() in which, the VCPU_KICK_SOFTIRQ
bit was set.

> IOW - shouldn't this setup be conditional, 

We cannot setup pi_notification_interrupt() conditional, since it is
for all cases, non-vtd-pi and vt-d pi.

> and shouldn't the handler also only conditionally raise the softirq
> (to as much as possible limit their amount)?

As mentioned above, there are not extra softirq raised. If you think
It is necessary, I can add a condition here as below, which I really think
is useless, but I am fine to add it if you really think it is a must.

        if ( iommu_intpost )
                raise_softirq(VCPU_KICK_SOFTIRQ);

Thanks,
Feng


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