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Date: Fri, 30 Sep 2016 13:40:11 +0800
From: Peter Xu <peterx@redhat.com>
Message-ID: <20160930054011.GN11134@pxdev.xzpeter.org>
References: <20160929112329.2408-1-rkrcmar@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 7/7] intel-iommu: keep buggy EIM enabled
 in 2.7 machine type
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To: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc: qemu-devel@nongnu.org, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

On Thu, Sep 29, 2016 at 01:23:29PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99 wro=
te:

[...]

> @@ -2481,11 +2482,14 @@ static void vtd_realize(DeviceState *dev, Error=
 **errp)
>      if (s->intr_eim =3D=3D ON_OFF_AUTO_AUTO && !x86_iommu->intr_suppor=
ted) {
>          s->intr_eim =3D ON_OFF_AUTO_OFF;
>      }
> +    if (s->intr_eim =3D=3D ON_OFF_AUTO_AUTO && pcmc->buggy_intel_iommu=
_eim) {
> +        s->intr_eim =3D ON_OFF_AUTO_ON;
> +    }
>      if (s->intr_eim =3D=3D ON_OFF_AUTO_AUTO) {
>          s->intr_eim =3D kvm_irqchip_in_kernel() ? ON_OFF_AUTO_ON
>                                                : ON_OFF_AUTO_OFF;
>      }
> -    if (s->intr_eim =3D=3D ON_OFF_AUTO_ON) {
> +    if (s->intr_eim =3D=3D ON_OFF_AUTO_ON && !pcmc->buggy_intel_iommu_=
eim) {
>          if (kvm_irqchip_in_kernel() && !kvm_enable_x2apic()) {
>              error_report("intel-iommu,eim=3Don requires support on the=
 KVM side "
>                           "(X2APIC_API, first shipped in v4.7).");

No matter how we would treat this patch, I see that we are stacking up
if clauses here. So IMHO maybe it's time to award EIM a new routine:

  int vtd_eim_detect(IntelIOMMUState *, Error **errp);

And squash all these conditions in. Then in vtd_realize():

  if (vtd_eim_detect(s, errp)) {
      return;
  }

Thanks,

-- peterx