[PATCH v17 14/19] PCI/CXL: Reject reset with unsafe function scope

[Srirangan Madhavan]

The per-device PCI reset interface must not reset sibling functions.
Reject cxl_reset and cxl_bus for VFs, multifunction devices, and PFs with
enabled VFs.

Suggested-by: Alex Williamson <alwilliamson@xxxxxxxxxx>
Link: https://lore.kernel.org/linux-cxl/20260626160846.426e71b6@xxxxxxxxxx/
Link: https://lore.kernel.org/linux-cxl/6a50441e2bb5e_3cabcb1003e@djbw-dev.notmuch/
Signed-off-by: Srirangan Madhavan <smadhavan@xxxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Richard Cheng <icheng@xxxxxxxxxx>

---
Changes in v17:
- Move the function-scope checks ahead of the CXL DVSEC lookups, so a VF
  returns -ENOTTY without config reads during reset-method probing
  (Joshua)
  https://lore.kernel.org/linux-cxl/20261105143611.31563-1-machaujo@xxxxxxxxx/
---
 drivers/pci/cxl.c | 3 +++
 drivers/pci/pci.c | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/pci/cxl.c b/drivers/pci/cxl.c
index af8ec8db20f1..c07266ab0133 100644
--- a/drivers/pci/cxl.c
+++ b/drivers/pci/cxl.c
@@ -501,6 +501,9 @@ int cxl_reset_function(struct pci_dev *pdev, bool probe)
 	u16 dvsec, cap, ctrl;
 	int rc;
 
+	if (pdev->is_virtfn || pdev->multifunction || pci_num_vf(pdev))
+		return -ENOTTY;
+
 	rc = cxl_pci_device_dvsec(pdev, &dvsec, &cap);
 	if (rc)
 		return rc;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b2879a6be5f8..aef976d0c850 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5018,6 +5018,13 @@ static int cxl_reset_bus_function(struct pci_dev *dev, bool probe)
 	u16 dvsec, reg, val;
 	int rc;
 
+	/*
+	 * Reject VFs and multifunction devices before walking the bridge's
+	 * capabilities: every VF behind the same bridge would repeat the walk.
+	 */
+	if (dev->is_virtfn || dev->multifunction || pci_num_vf(dev))
+		return -ENOTTY;
+
 	bridge = pci_upstream_bridge(dev);
 	if (!bridge)
 		return -ENOTTY;
-- 
2.43.0