On 09/19/2017 03:24 AM, Wuzongyong (Euler Dept) wrote:
> 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?
Yes. I mean, sort of. Obviously we haven't encountered platform with
multiple PCHs yet.
Michal
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