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 <wda...@nvidia.com>
---
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)) {
+ /*
+ * 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;
+
+ /*
+ * 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
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
