Re: [Xen-devel] [PATCH v4] VT-d: fix VF of RC integrated PF matched to wrong VT-d unit

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Gao, Chao
> Sent: Monday, July 3, 2017 12:37 PM
> 
> On Fri, Jun 30, 2017 at 05:19:52PM +0800, Tian, Kevin wrote:
> >> From: Gao, Chao
> >> Sent: Friday, June 30, 2017 9:17 AM
> >>
> >> The problem is for a VF of RC integrated PF (e.g. PF's BDF is 00:02.0),
> >> we would wrongly use 00:00.0 to search VT-d unit.
> >>
> >> From SRIOV spec REV 1.0 section 3.7.3, it says:
> >> "ARI is not applicable to Root Complex integrated Endpoints; all other
> >> SR-IOV Capable Devices (Devices that include at least one PF) shall
> >> implement the ARI Capability in each Function.". So PFs can be classified
> to
> >> two kinds: one is RC integrated PF and the other is non-RC integrated PF.
> The
> >> former can't support ARI and the latter shall support ARI. For Extended
> >> Functions, one traditional function's BDF should be used to search VT-d
> unit.
> >> And according to PCIe spec, Extened Function means within an ARI device,
> a
> >> Function whose Function Number is greater than 7. Thus, the former can't
> be
> >> an
> >> extended function, while the latter is as long as its devfn > 7, this 
> >> check is
> >> exactly what the original code did; The original code wasn't aware the
> former.
> >>
> >> This patch directly looks up the 'is_extfn' field of PF's struct pci_dev
> >> to decide whether the PF is a extended function.
> >
> >Above description looks like the bug is caused by ARI problem. But
> >if you look at the original code (and the problem you described), it's
> >not related to ARI. ARI comes just when adding a clean fix, so please
> >revise the description to make that part clear
> >
> 
> How about this:
> 
> The problem is for a VF of RC integrated PF (e.g. PF's BDF is 00:02.0),
> we would wrongly use 00:00.0 to search VT-d unit.
> 
> If a PF is an extended function, a traditional function's BDF should be
> used to search VT-d unit. Previous code only checks whether Function
> Number is greater than 7, without checking the prerequisite that the

where did above check come from in original code? 

-        devfn = PCI_SLOT(pdev->info.physfn.devfn) ? 0 : 
pdev->info.physfn.devfn;

> function should be within an ARI device. This incurs wrongly using
> traditional function's BDF when the PF is RC integrated and thus cannot
> be within an ARI device.
> 
> Considering 'is_extfn' field of struct pci_dev has been passed down from
> Domain0 to indicate whether the function is an extended function, this
> patch just looks up that field of PF's struct pci_dev and adjust BDF
> used to search VT-d unit accordingly.
> 

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