On Mon, May 04, 2020 at 12:52:53PM -0600, Alex Williamson wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, 4 May 2020 18:09:16 +0200
> Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
>
> > On Fri, 01 May 2020 15:41:24 -0600
> > Alex Williamson <alex.williamson@xxxxxxxxxx> wrote:
> >
> > > There is no PCI spec defined capability with ID 0, therefore we don't
> > > expect to find it in a capability chain and we use this index in an
> > > internal array for tracking the sizes of various capabilities to handle
> > > standard config space. Therefore if a device does present us with a
> > > capability ID 0, we mark our capability map with nonsense that can
> > > trigger conflicts with other capabilities in the chain. Ignore ID 0
> > > when walking the capability chain, handling it as a hidden capability.
> > >
> > > Seen on an NVIDIA Tesla T4.
> > >
> > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > > ---
> > > drivers/vfio/pci/vfio_pci_config.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> > > index 87d0cc8c86ad..5935a804cb88 100644
> > > --- a/drivers/vfio/pci/vfio_pci_config.c
> > > +++ b/drivers/vfio/pci/vfio_pci_config.c
> > > @@ -1487,7 +1487,7 @@ static int vfio_cap_init(struct vfio_pci_device *vdev)
> > > if (ret)
> > > return ret;
> > >
> > > - if (cap <= PCI_CAP_ID_MAX) {
> >
> > Maybe add a comment:
> >
> > /* no PCI spec defined capability with ID 0: hide it */
Hi Alex,
I think this is NULL Capability defined in Codes and IDs spec, probably we
should just add a new enum to represent that?
Thanks,
Neo
> >
>
> Sure.
>
> >
> > > + if (cap && cap <= PCI_CAP_ID_MAX) {
> > > len = pci_cap_length[cap];
> > > if (len == 0xFF) { /* Variable length */
> > > len = vfio_cap_len(vdev, cap, pos);
> > >
> >
> > Is there a requirement for caps to be strictly ordered? If not, could
> > len hold a residual value from a previous iteration?
>
> There is no ordering requirement for capabilities, but len is declared
> non-static with an initial value within the scope of the loop, it's
> reset every iteration. Thanks,
>
> Alex
>
