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

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

[Jintack Lim]

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?

Thanks,
Jintack

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

[Jintack Lim]

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?
>
> Thanks,
> Jintack

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

[Alex Williamson]

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

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

[Jintack Lim]

On Mon, Apr 30, 2018 at 2:09 PM, Alex Williamson
<alex.williamson@redhat.com> wrote:
> 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
>

Thanks for a nice solution, Alex.
It turns out my cpu doesn't have the PI capability.
/sys/class/iommu/dmar0: 0
/sys/class/iommu/dmar1: 0

> 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,

Yeah, I think that makes sense.

Thanks,
Jintack

>
> Alex
>