Re: [PATCH 4/4] pci: Compare function number and ARI next function number

[Akihiko Odaki]

On 2023/07/02 13:58, Michael S. Tsirkin wrote:
> On Sat, Jul 01, 2023 at 04:01:22PM +0900, Akihiko Odaki wrote:
> > The function number must be lower than the next function number
> > advertised with ARI.
> >
> > Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>
> I don't get this logic at all - where is the limitation coming from?
>
> All I see in the spec is:
>         Next Function Number - With non-VFs, this field indicates the Function 
> Number of the next higher
>         numbered Function in the Device, or 00h if there are no higher numbered 
> Functions. Function 0 starts
>         this linked list of Functions.
>         The presence of Shadow Functions does not affect this field.
>         For VFs, this field is undefined since VFs are located using First VF 
> Offset (see § Section 9.3.3.9 ) and VF
>         Stride (see § Section 9.3.3.10 ).
>
> and
>
>          To improve the enumeration performance and create a more deterministic 
> solution, software can
>         enumerate Functions through a linked list of Function Numbers. The next 
> linked list element is
>         communicated through each Function’s ARI Capability Register.
>         i. Function 0 acts as the head of a linked list of Function Numbers. 
> Software detects a
>         non-Zero Next Function Number field within the ARI Capability Register 
> as the next
>         Function within the linked list. Software issues a configuration probe 
> using the Bus Number
>         captured by the Device and the Function Number derived from the ARI 
> Capability Register
>         to locate the next associated Function’s configuration space.
>         ii. Function Numbers may be sparse and non-sequential in their 
> consumption by an ARI
>         Device.

The statement "With non-VFs, this field indicates the Function Number of 
the next higher numbered Function in the Device, or 00h if there are no 
higher numbered Functions." implies the Function Number of the device 
should be lower than the value advertised by the field (for non-VFs; 
this patch does not check if it's VF or not.)

> > ---
> >   hw/pci/pci.c | 15 +++++++++++++++
> >   1 file changed, 15 insertions(+)
> >
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index e2eb4c3b4a..568665ee42 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -2059,6 +2059,8 @@ static void pci_qdev_realize(DeviceState *qdev, Error 
> > **errp)
> >       Error *local_err = NULL;
> >       bool is_default_rom;
> >       uint16_t class_id;
> > +    uint16_t ari;
> > +    uint16_t nextfn;
> >   
> >       /*
> >        * capped by systemd (see: udev-builtin-net_id.c)
> > @@ -2121,6 +2123,19 @@ static void pci_qdev_realize(DeviceState *qdev, Error 
> > **errp)
> >           }
> >       }
> >   
> > +    if (pci_is_express(pci_dev)) {
> > +        ari = pcie_find_capability(pci_dev, PCI_EXT_CAP_ID_ARI);
> > +        if (ari) {
> > +            nextfn = (pci_get_long(pci_dev->config + ari + PCI_ARI_CAP) >> 8) 
> > & 0xff;
> > +            if (nextfn && (pci_dev->devfn & 0xff) >= nextfn) {
> > +                error_setg(errp, "PCI: function number %u is not lower than ARI 
> > next function number %u",
> > +                           pci_dev->devfn & 0xff, nextfn);
> > +                pci_qdev_unrealize(DEVICE(pci_dev));
> > +                return;
> > +            }
> > +        }
> > +    }
> > +
> >       if (pci_dev->failover_pair_id) {
> >           if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
> >               error_setg(errp, "failover primary device must be on "
> > --
> > 2.41.0