[PATCH v11 04/13] PCI: Allow PASID only when ACS enforced on upstreaming path

[Lu Baolu]

Some configurations of the PCI fabric will route device originated TLP
packets based on the memory addresses. These configurations are
incompatible with PASID as the PASID packets form a distinct address
space. For instance, any configuration where switches are present
without ACS enabled is incompatible.

This enhances the pci_enable_pasid() interface by requiring the ACS to
support Source Validation, Request Redirection, Completer Redirection,
and Upstream Forwarding. This effectively means that devices cannot
spoof their requester ID, requests and completions cannot be redirected,
and all transactions are forwarded upstream, even as it passes through a
bridge where the target device is downstream.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Suggested-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/pci/ats.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index c967ad6e2626..0715e48e7973 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -382,6 +382,11 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
 	if (!pasid)
 		return -EINVAL;
 
+	if (!pci_acs_path_enabled(pdev, NULL,
+				  PCI_ACS_SV | PCI_ACS_RR |
+				  PCI_ACS_CR | 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