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SubjectRe: [PATCH] vfio/pci: Add extra test for extended capabilities
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On Thu, 2014-06-12 at 16:12 -0400, Bandan Das wrote:
> Alex Williamson <alex.williamson@redhat.com> writes:
>
> > If the PCI core set cfg_size isn't large enough for extended
> > capabilities, then they're not there. Extended config space may be
> > inaccessible due to a PCI bridge, in which case cfg_size may be cut
> > short.
>
> Just curious, is this part of the spec or just a convention ? I mean
> could there be devices with quirks ?

The PCIe bridge spec indicates that PCIe-to-PCI bridges should handle
extended config accesses as an unsupported request. But as in 78916b00,
we've seen that's not always the case. This just makes us trust
PCI-core before the capabilities we find on the device. The current
quirk in the referenced commit is for a relatively uncommon topology,
but never rule out that we couldn't have a device quirked to avoid
touching extended config space too. Thanks,

Alex

> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > ---
> > drivers/vfio/pci/vfio_pci_config.c | 13 +++++++++----
> > 1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> > index 83cd157..4a62a37 100644
> > --- a/drivers/vfio/pci/vfio_pci_config.c
> > +++ b/drivers/vfio/pci/vfio_pci_config.c
> > @@ -1027,8 +1027,11 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
> >
> > if (PCI_X_CMD_VERSION(word)) {
> > /* Test for extended capabilities */
> > - pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> > - vdev->extended_caps = (dword != 0);
> > + if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
> > + pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE,
> > + &dword);
> > + vdev->extended_caps = (dword != 0);
> > + }
> > return PCI_CAP_PCIX_SIZEOF_V2;
> > } else
> > return PCI_CAP_PCIX_SIZEOF_V0;
> > @@ -1041,8 +1044,10 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
> > return byte;
> > case PCI_CAP_ID_EXP:
> > /* Test for extended capabilities */
> > - pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> > - vdev->extended_caps = (dword != 0);
> > + if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
> > + pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> > + vdev->extended_caps = (dword != 0);
> > + }
> >
> > /* length based on version */
> > if ((pcie_caps_reg(pdev) & PCI_EXP_FLAGS_VERS) == 1)
> >
> > --
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