linux-kernel - [PATCH] PCI: Do not enable PASID when End-to-End TLP is not supported

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Date:   Sat, 19 May 2018 12:52:49 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-pci@...r.kernel.org, timur@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] PCI: Do not enable PASID when End-to-End TLP is not supported

A PCIe endpoint carries the process address space identifier (PASID) in
the TLP prefix as part of the memory read/write transaction. The address
information in the TLP is relevant only for a given PASID context.

A translation agent takes PASID value and the address information from the
TLP to look up the physical address in the system.

If a bridge drops the TLP prefix, the translation agent can resolve the
address to an incorrect location and cause data corruption. Prevent
this condition by requiring End-to-End TLP prefix to be supported on the
entire data path between the endpoint and the root port.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/pci/ats.c             | 16 ++++++++++++++++
 include/uapi/linux/pci_regs.h |  1 +
 2 files changed, 17 insertions(+)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index 89305b5..0bcded5 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -265,7 +265,9 @@ EXPORT_SYMBOL_GPL(pci_reset_pri);
 int pci_enable_pasid(struct pci_dev *pdev, int features)
 {
 	u16 control, supported;
+	struct pci_dev *bridge;
 	int pos;
+	u32 cap;
 
 	if (WARN_ON(pdev->pasid_enabled))
 		return -EBUSY;
@@ -274,6 +276,20 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
 	if (!pos)
 		return -EINVAL;
 
+	bridge = pci_upstream_bridge(pdev);
+	while (bridge) {
+		if (!pci_find_capability(bridge, PCI_CAP_ID_EXP))
+			return -EINVAL;
+
+		if (pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap))
+			return -EINVAL;
+
+		if (!(cap & PCI_EXP_DEVCAP2_E2ETLP))
+			return -EINVAL;
+
+		bridge = pci_upstream_bridge(bridge);
+	}
+
 	pci_read_config_word(pdev, pos + PCI_PASID_CAP, &supported);
 	supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
 
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index 103ba79..d91dea5 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -634,6 +634,7 @@
 #define  PCI_EXP_DEVCAP2_OBFF_MASK	0x000c0000 /* OBFF support mechanism */
 #define  PCI_EXP_DEVCAP2_OBFF_MSG	0x00040000 /* New message signaling */
 #define  PCI_EXP_DEVCAP2_OBFF_WAKE	0x00080000 /* Re-use WAKE# for OBFF */
+#define PCI_EXP_DEVCAP2_E2ETLP		0x00200000 /* End-to-End TLP Prefix */
 #define PCI_EXP_DEVCTL2		40	/* Device Control 2 */
 #define  PCI_EXP_DEVCTL2_COMP_TIMEOUT	0x000f	/* Completion Timeout Value */
 #define  PCI_EXP_DEVCTL2_COMP_TMOUT_DIS	0x0010	/* Completion Timeout Disable */
-- 
2.7.4