On Tue, Sep 15, 2015 at 12:10:54PM -0500, Will Davis wrote:
> Add checks for topology and ACS configuration to determine whether or not
> peer traffic should be supported between two PCI devices.
>
> Signed-off-by: Will Davis <wdavis@xxxxxxxxxx>
> ---
> drivers/pci/pci.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 3 ++
> 2 files changed, 102 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 0008c95..b8ba0f0 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -25,6 +25,7 @@
> #include <linux/device.h>
> #include <linux/pm_runtime.h>
> #include <linux/pci_hotplug.h>
> +#include <linux/iommu.h>
> #include <asm-generic/pci-bridge.h>
> #include <asm/setup.h>
> #include "pci.h"
> @@ -4302,6 +4303,104 @@ void pci_ignore_hotplug(struct pci_dev *dev)
> }
> EXPORT_SYMBOL_GPL(pci_ignore_hotplug);
>
> +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;
> +
> + if (pci_is_pcie(dev) && pci_is_pcie(peer)) {
Can you use the same "return errors early" trick here to unindent
everything below, e.g.,
if (!pci_is_pcie(dev) || !pci_is_pcie(peer))
return false;
> + /*
> + * 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;
This will oops if rpdev or rppeer is a VF on a "virtual" bus (bus->self
is NULL in that case); see the comment near pci_is_root_bus().
> + 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;
I think we might need some sort of pcie_root_port() function. We already
have a static pcie_find_root_port() that is basically the same. And
dmar_find_matched_atsr_unit() does something very similar. And
ixgbe_io_error_detected(). And myri10ge_enable_ecrc().
> +
> + 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);
This (and the ACS check) logically belongs above the rpdev/rppeer stuff.
> + /*
> + * 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;
> +
> + /*
> + * 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 */
> --
> 2.5.1
>
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