[PATCH v12 04/17] PCI: Enable PASID only when ACS RR & UF enabled on upstream path

[Lu Baolu <baolu.lu@linux.intel.com>]

The Requester ID/Process Address Space ID (PASID) combination
identifies an address space distinct from the PCI bus address space,
e.g., an address space defined by an IOMMU.

But the PCIe fabric routes Memory Requests based on the TLP address,
ignoring any PASID (PCIe r6.0, sec 2.2.10.4), so a TLP with PASID that
SHOULD go upstream to the IOMMU may instead be routed as a P2P
Request if its address falls in a bridge window.

To ensure that all Memory Requests with PASID are routed upstream,
only enable PASID if ACS P2P Request Redirect and Upstream Forwarding
are enabled for the path leading to the device.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Suggested-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Tony Zhu <tony.zhu@intel.com>
---
 drivers/pci/ats.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index c967ad6e2626..f9cc2e10b676 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -382,6 +382,9 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
 	if (!pasid)
 		return -EINVAL;
 
+	if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
+		return -EINVAL;
+
 	pci_read_config_word(pdev, pasid + PCI_PASID_CAP, &supported);
 	supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
 
-- 
2.25.1