Re: [Qemu-devel] How to check if Vt-d is capable of posted-interrupt?

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 30 Apr 2018 13:44:23 -0400
Jintack Lim <jintack@cs.columbia.edu> wrote:

> Add iommu mailing list since this question might be more related to iommu.
> 
> On Mon, Apr 30, 2018 at 10:11 AM, Jintack Lim <jintack@cs.columbia.edu> wrote:
> > Hi,
> >
> > I wonder how to check if Vt-d is capable of posted-interrupt? I'm
> > using Intel E5-2630 v3.
> >
> > I was once told that APICv and posted-interrupt capability always come
> > together. But it seems like my cpu support APICv
> > (/sys/module/kvm_intel/parameters/enable_apicv is Y), but
> > posted-interrupt capability is only shipped with the next generation
> > of the cpu (E5-2600 v4, which is Broadwell).
> >
> > What would be an easy way to check this?

PI support is bit 59 in the capability register which is exposed
through sysfs at /sys/class/iommu/dmar*/intel-iommu/cap so you could do
something like:

# for i in $(find /sys/class/iommu/dmar* -type l); do echo -n "$i: "; echo $(( ( 0x$(cat $i/intel-iommu/cap) >> 59 ) & 1 )); done

I think the relationship between APICv and PI goes the other direction,
if you have PI, you probably have APICv.  Having APICv implies nothing
about having PI.  Thanks,

Alex