On Tue, 2015-09-15 at 12:10 -0500, Will Davis wrote:
> +bool pci_peer_traffic_supported(struct pci_dev *dev, struct pci_dev
> *peer)
> +{
> +> > struct pci_host_bridge *dev_host_bridge;
> +> > struct pci_host_bridge *peer_host_bridge;
> +
> +> > /*
> +> > * Disallow the peer-to-peer traffic if the devices do not share a
> +> > * host bridge. The PCI specifications does not make any guarantees
> +> > * about P2P capabilities between devices under separate domains.
> +> > *
> +> > * PCI Local Bus Specification Revision 3.0, section 3.10:
> +> > * "Peer-to-peer transactions crossing multiple host bridges
> +> > * PCI host bridges may, but are not required to, support PCI
> +> > * peer-to-peer transactions that traverse multiple PCI host
> +> > * bridges."
> +> > */
> + dev_host_bridge = pci_find_host_bridge(dev->bus);
> +> > peer_host_bridge = pci_find_host_bridge(peer->bus);
> +> > if (dev_host_bridge != peer_host_bridge)
> +> > > return false;
This needs to be platform specific. Some architectures will allow
routing between multiple bridges, some won't.
> + /*
> +> > > * Access Control Services (ACS) Checks
> +> > > *
> +> > > * ACS has a capability bit for P2P Request Redirects (RR),
> +> > > * but unfortunately it doesn't tell us much about the real
> +> > > * capabilities of the hardware.
> +> > > *
> +> > > * PCI Express Base Specification Revision 3.0, section
> +> > > * 6.12.1.1:
> +> > > * "ACS P2P Request Redirect: must be implemented by Root
> +> > > * Ports that support peer-to-peer traffic with other
> +> > > * Root Ports; [80]"
> +> > > * but
> +> > > * "[80] Root Port indication of ACS P2P Request Redirect
> +> > > * or ACS P2P Completion Redirect support does not imply
> +> > > * any particular level of peer-to-peer support by the
> +> > > * Root Complex, or that peer-to-peer traffic is
> +> > > * supported at all"
> +> > > */
> +> > > struct pci_dev *rpdev = dev->bus->self;
> +> > > struct pci_dev *rppeer = peer->bus->self;
> +> > > struct pci_dev *common_upstream;
> +> > > int pos;
> +> > > u16 cap;
> +
> +> > > while ((rpdev) && (pci_is_pcie(rpdev)) &&
> +> > > (pci_pcie_type(rpdev) != PCI_EXP_TYPE_ROOT_PORT))
> +> > > > rpdev = rpdev->bus->self;
> +
> +> > > while ((rppeer) && (pci_is_pcie(rppeer)) &&
> +> > > (pci_pcie_type(rppeer) != PCI_EXP_TYPE_ROOT_PORT))
> +> > > > rppeer = rppeer->bus->self;
> +
> +> > > common_upstream = pci_find_common_upstream_dev(dev, peer);
> +
> +> > > /*
> +> > > * If ACS is not implemented, we have no idea about P2P
> +> > > * support. Optimistically allow this if there is a common
> +> > > * upstream device.
> +> > > */
> +> > > pos = pci_find_ext_capability(rpdev, PCI_EXT_CAP_ID_ACS);
> +> > > if (!pos)
> +> > > > return common_upstream != NULL;
We might need a hook as well here. PLX switch may or may not allow it
depending on some configuration bits.
> + /*
> +> > > * If the devices are under the same root port and have a
> common
> +> > > * upstream device, allow if the root port is further upstream
> +> > > * from the common upstream device and the common upstream
> +> > > * device has Upstream Forwarding disabled, or if the root
> port
> +> > > * is the common upstream device and ACS is not implemented.
> +> > > */
> +> > > pci_read_config_word(rpdev, pos + PCI_ACS_CAP, &cap);
> +> > > if ((rpdev == rppeer && common_upstream) &&
> +> > > (((common_upstream != rpdev) &&
> +> > > !pci_acs_enabled(common_upstream, PCI_ACS_UF)) ||
> +> > > ((common_upstream == rpdev) && ((cap & PCI_ACS_RR) ==
> 0))))
> +> > > > return true;
> +
> +> > > /*
> +> > > * If ACS RR is implemented and disabled, allow only if the
> +> > > * devices are under the same root port.
> +> > > */
> +> > > if (cap & PCI_ACS_RR && !pci_acs_enabled(rpdev, PCI_ACS_RR))
> +> > > > return rpdev == rppeer;
> +
> +> > > /*
> +> > > * If ACS RR is not implemented, or is implemented and
> enabled,
> +> > > * only allow if there's a translation agent enabled to do the
> +> > > * redirect.
> +> > > */
> +> > > return iommu_present(&pci_bus_type);
> +> > }
> +
> +> > return false;
> +}
> +
> #define RESOURCE_ALIGNMENT_PARAM_SIZE COMMAND_LINE_SIZE
> static char resource_alignment_param[RESOURCE_ALIGNMENT_PARAM_SIZE] = {0};
> static DEFINE_SPINLOCK(resource_alignment_lock);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 8262b9e..db0cb51 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -824,6 +824,8 @@ void pci_stop_root_bus(struct pci_bus *bus);
> void pci_remove_root_bus(struct pci_bus *bus);
> void pci_setup_cardbus(struct pci_bus *bus);
> void pci_sort_breadthfirst(void);
> +bool pci_peer_traffic_supported(struct pci_dev *dev, struct pci_dev *peer);
> +
> #define dev_is_pci(d) ((d)->bus == &pci_bus_type)
> #define dev_is_pf(d) ((dev_is_pci(d) ? to_pci_dev(d)->is_physfn : false))
> #define dev_num_vf(d) ((dev_is_pci(d) ? pci_num_vf(to_pci_dev(d)) : 0))
> @@ -1914,4 +1916,5 @@ static inline bool pci_ari_enabled(struct pci_bus *bus)
> {
> > > return bus->self && bus->self->ari_enabled;
> }
> +
> #endif /* LINUX_PCI_H */
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