Hi,

In function virPCIDeviceIsBehindSwitchLackingACS, I noticed that(line 8):

1    if (virPCIDeviceGetParent(dev, &parent) < 0)

2        return -1;

3    if (!parent) {

4        /* if we have no parent, and this is the root bus, ACS doesn't come

5         * into play since devices on the root bus can't P2P without going

6         * through the root IOMMU.

7         */

8        if (dev->address.bus == 0) {

9            return 0;

10        } else {

11            virReportError(VIR_ERR_INTERNAL_ERROR,

12                           _("Failed to find parent device for %s"),

13                           dev->name);

14            return -1;

15        }

16    }

Why we just return 0 only if device’s bus is 0?

In my server, I can see a root bus which bus number is greater than 0, see the

results(just a part) after I run lspci -t:

+-[0000:80]-+-02.0-[81-83]--+-00.0

|           |               \-00.1

|           +-05.0

|           +-05.1

|           +-05.2

|           \-05.4

+-[0000:7f]-+-08.0

|           +-08.2

|           +-08.3

|           + . . .

|           \-1f.2

\-[0000:00]-+-00.0

             +-01.0-[01]----00.0

             +-02.0-[02]--+-00.0

             |            +-00.1

             |            +-00.2

             |            \-00.3

             +-02.2-[03]--

             +-03.0-[04-0b]----00.0-[05-0b]--+-08.0-[06-08]----00.0

             |                               \-10.0-[09-0b]----00.0

             +-05.0

             +-05.1

             +-05.2

             +-05.4

             +-11.0

             +-11.4

             +-16.0

             +-16.1

             +-1a.0

If I assign the device 0000:81:00.0 to a VM, I get “Failed to find parent device”.

I think I should get no error with return value 0 just like bus number is 0, because

bus 80 is the root bus as well in my case.

In the <<Intel C610 Series Chipset and Intel X99 Chipset Platform Controller Hub(PCH)>>

Datasheet, I found that(Chapter 9.1):

For some server platforms, it may be desirable to have multiple PCHs in the system

Which means some PCH’s may reside on a bus greater than 0.

So, is this a bug?

Thanks,

Zongyong Wu