[PATCH] enabling ACS P2P upstream forwarding

[Kay, Allen M]

This patch enables P2P upstream forwarding in ACS capable PCIe switches.  This solves two potential problems in virtualization environment where a PCIe device is assigned to a guest domain using a HW iommu such as VT-d:

1) Unintentional failure caused by guest physical address programmed into the device's DMA that happens to match the memory address range of other downstream ports in the same PCIe switch.  This causes the PCI transaction to go to the matching downstream port instead of go to the root complex to get translated by VT-d as it should be.

2) Malicious guest software intentionally attacks another downstream PCIe device by programming the DMA address into the assigned device that matches memory address range of the downstream PCIe port.

We are in process of implementing device filtering software in KVM/XEN management software to allow device assignment of PCIe devices behind a PCIe switch only if it has ACS capability and with the P2P upstream forwarding bits enabled.  This patch is intended to work for both KVM and Xen environments.

Signed-off-by: Allen Kay allen.m.kay@xxxxxxxxx

---

 drivers/pci/pci.c        |   37 +++++++++++++++++++++++++++++++++++++
 drivers/pci/pci.h        |    1 +
 drivers/pci/probe.c      |    3 +++
 include/linux/pci_regs.h |   14 ++++++++++++++
 4 files changed, 55 insertions(+)

=================================================================

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7b70312..e70abde 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1513,6 +1513,49 @@ void pci_enable_ari(struct pci_dev *dev)
 }
 
 /**
+ * pci_acs_enable - enable ACS if hardware support it
+ * @dev: the PCI device
+ */
+#define ACS_ENABLED (PCI_EXP_ACS_V|PCI_EXP_ACS_R|PCI_EXP_ACS_C|PCI_EXP_ACS_U)
+void pci_acs_init(struct pci_dev *dev)
+{
+	int pos;
+	u16 cap;
+	u16 ctrl;
+
+	if (!dev->is_pcie)
+		return;
+
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
+	if (!pos)
+		return;
+
+	pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
+	if ((cap & ACS_ENABLED) != ACS_ENABLED)
+		dev_info(&dev->dev, "ACS P2P upstream not supported\n");
+
+	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
+
+	/* Source Validation */
+	if (cap & PCI_EXP_ACS_V)
+		ctrl |= PCI_EXP_ACS_V;
+
+	/* P2P Request Redirect */
+	if (cap & PCI_EXP_ACS_R)
+		ctrl |= PCI_EXP_ACS_R;
+
+	/* P2P Completion Redirect */
+	if (cap & PCI_EXP_ACS_C)
+		ctrl |= PCI_EXP_ACS_C;
+
+	/* Upstream Forwarding */
+	if (cap & PCI_EXP_ACS_U)
+		ctrl |= PCI_EXP_ACS_U;
+
+	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
+}
+
+/**
  * pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
  * @dev: the PCI device
  * @pin: the INTx pin (1=INTA, 2=INTB, 3=INTD, 4=INTD)
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 5ff4d25..1d8976d 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -202,6 +202,7 @@ static inline int pci_ari_enabled(struct pci_bus *bus)
 {
 	return bus->self && bus->self->ari_enabled;
 }
+extern void pci_acs_init(struct pci_dev *dev);
 
 #ifdef CONFIG_PCI_QUIRKS
 extern int pci_is_reassigndev(struct pci_dev *dev);
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 40e75f6..4a5ec9e 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -991,6 +991,9 @@ static void pci_init_capabilities(struct pci_dev *dev)
 
 	/* Single Root I/O Virtualization */
 	pci_iov_init(dev);
+
+	/* Access Control Service */
+	pci_acs_init(dev);
 }
 
 void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
diff --git a/include/linux/pci_regs.h b/include/linux/pci_regs.h
index fcaee42..90014ad 100644
--- a/include/linux/pci_regs.h
+++ b/include/linux/pci_regs.h
@@ -492,6 +492,14 @@
 #define PCI_EXP_LNKCTL2		48	/* Link Control 2 */
 #define PCI_EXP_SLTCTL2		56	/* Slot Control 2 */
 
+#define  PCI_EXP_ACS_V		0x01	/* Source Validation */
+#define  PCI_EXP_ACS_B		0x02	/* Translation Blocking */
+#define  PCI_EXP_ACS_R		0x04	/* P2P Request Redirect */
+#define  PCI_EXP_ACS_C		0x08	/* P2P Completion Redirect */
+#define  PCI_EXP_ACS_U		0x10	/* Upstream Forwarding */
+#define  PCI_EXP_ACS_E		0x20	/* P2P Egress Control */
+#define  PCI_EXP_ACS_T		0x40	/* Direct Translated P2P */
+
 /* Extended Capabilities (PCI-X 2.0 and Express) */
 #define PCI_EXT_CAP_ID(header)		(header & 0x0000ffff)
 #define PCI_EXT_CAP_VER(header)		((header >> 16) & 0xf)
@@ -501,6 +509,7 @@
 #define PCI_EXT_CAP_ID_VC	2
 #define PCI_EXT_CAP_ID_DSN	3
 #define PCI_EXT_CAP_ID_PWR	4
+#define PCI_EXT_CAP_ID_ACS	13
 #define PCI_EXT_CAP_ID_ARI	14
 #define PCI_EXT_CAP_ID_ATS	15
 #define PCI_EXT_CAP_ID_SRIOV	16
@@ -661,4 +670,9 @@
 #define  PCI_SRIOV_VFM_MO	0x2	/* Active.MigrateOut */
 #define  PCI_SRIOV_VFM_AV	0x3	/* Active.Available */
 
+/* Access Control Service */
+#define PCI_ACS_CAP		0x04	/* ACS Capability Register */
+#define PCI_ACS_CTRL		0x06	/* ACS Control Register */
+#define PCI_ACS_EGRESS_CTL_V	0x08	/* ACS Egress Control Vector */
+
 #endif /* LINUX_PCI_REGS_H */

Attachment: acs0915.patch
Description: acs0915.patch