[PATCH 1/3] PCI: Add check for CXL Secondary Bus Reset

[Dave Jiang <dave.jiang@xxxxxxxxx>]

Per CXL spec r3.1 8.1.5.2, secondary bus reset is masked unless the
"Unmask SBR" bit is set. Add a check to the PCI secondary bus reset
path to fail the CXL SBR request if the "Unmask SBR" bit is clear in
the CXL Port Control Extensions regiser by returning -EPERM.

The expectation is that if a user overrides the "Unmask SBR" via a
user tool such as setpci, they can trigger a bus reset after that.

Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
---
 drivers/cxl/cxlpci.h          |  2 --
 drivers/pci/pci.c             | 45 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/pci_regs.h |  7 ++++++
 3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
index 711b05d9a370..8d7952d7ca59 100644
--- a/drivers/cxl/cxlpci.h
+++ b/drivers/cxl/cxlpci.h
@@ -13,10 +13,8 @@
  * "DVSEC" redundancies removed. When obvious, abbreviations may be used.
  */
 #define PCI_DVSEC_HEADER1_LENGTH_MASK	GENMASK(31, 20)
-#define PCI_DVSEC_VENDOR_ID_CXL		0x1E98
 
 /* CXL 2.0 8.1.3: PCIe DVSEC for CXL Device */
-#define CXL_DVSEC_PCIE_DEVICE					0
 #define   CXL_DVSEC_CAP_OFFSET		0xA
 #define     CXL_DVSEC_MEM_CAPABLE	BIT(2)
 #define     CXL_DVSEC_HDM_COUNT_MASK	GENMASK(5, 4)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index c3585229c12a..5e5550f54053 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5347,10 +5347,55 @@ static int pci_dev_reset_slot_function(struct pci_dev *dev, bool probe)
 	return pci_reset_hotplug_slot(dev->slot->hotplug, probe);
 }
 
+static bool is_cxl_device(struct pci_dev *dev)
+{
+	return pci_find_dvsec_capability(dev, PCI_DVSEC_VENDOR_ID_CXL,
+					 CXL_DVSEC_PCIE_DEVICE);
+}
+
+static bool is_cxl_port_sbr_masked(struct pci_dev *dev)
+{
+	int dvsec;
+	int rc;
+	u16 reg;
+
+	/*
+	 * No DVSEC found, must not be CXL port.
+	 */
+	dvsec = pci_find_dvsec_capability(dev, PCI_DVSEC_VENDOR_ID_CXL,
+					  CXL_DVSEC_PCIE_PORT);
+	if (!dvsec)
+		return false;
+
+	rc = pci_read_config_word(dev, dvsec + CXL_DVSEC_PORT_CONTROL, &reg);
+	if (rc)
+		return true;
+
+	/*
+	 * CXL spec r3.1 8.1.5.2
+	 * When 0, SBR bit in Bridge Control register of this Port has no effect.
+	 * When 1, the Port shall generate hot reset when SBR bit in Bridge
+	 * Control gets set to 1.
+	 */
+	if (reg & CXL_DVSEC_PORT_CONTROL_UNMASK_SBR)
+		return false;
+
+	return true;
+}
+
 static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
 {
 	int rc;
 
+	/* If it's a CXL port and the SBR control is masked, fail the SBR */
+	if (is_cxl_device(dev) && dev->bus->self &&
+	    is_cxl_port_sbr_masked(dev->bus->self)) {
+		if (probe)
+			return 0;
+
+		return -EPERM;
+	}
+
 	rc = pci_dev_reset_slot_function(dev, probe);
 	if (rc != -ENOTTY)
 		return rc;
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index a39193213ff2..5f2c66987299 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -1148,4 +1148,11 @@
 #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL		0x00ff0000
 #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX	0xff000000
 
+/* Compute Express Link (CXL) */
+#define PCI_DVSEC_VENDOR_ID_CXL				0x1e98
+#define CXL_DVSEC_PCIE_DEVICE				0
+#define CXL_DVSEC_PCIE_PORT				3
+#define CXL_DVSEC_PORT_CONTROL				0x0c
+#define  CXL_DVSEC_PORT_CONTROL_UNMASK_SBR		0x00000001
+
 #endif /* LINUX_PCI_REGS_H */
-- 
2.44.0