[PATCH v2 18/20] vfio/cxl: Provide opt-out for CXL feature

[<mhonap@nvidia.com>]

From: Manish Honap <mhonap@nvidia.com>

This commit provides an opt-out mechanism to disable the CXL
support from vfio module. The opt-out is provided both
build time and module load time.

Build time option CONFIG_VFIO_CXL_CORE is used to enable/disable
CXL support in vfio-pci module.

For runtime disabling the CXL support, use the module parameter
disable_cxl. This is a per-device opt-out on the core device
set by the driver before registration.

Signed-off-by: Manish Honap <mhonap@nvidia.com>
---
 drivers/vfio/pci/cxl/vfio_cxl_core.c | 4 ++++
 drivers/vfio/pci/vfio_pci.c          | 9 +++++++++
 include/linux/vfio_pci_core.h        | 1 +
 3 files changed, 14 insertions(+)

diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c b/drivers/vfio/pci/cxl/vfio_cxl_core.c
index 46430cbfa962..3ffc3e593d04 100644
--- a/drivers/vfio/pci/cxl/vfio_cxl_core.c
+++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c
@@ -479,6 +479,10 @@ void vfio_pci_cxl_detect_and_init(struct vfio_pci_core_device *vdev)
 	u16 dvsec;
 	int ret;
 
+	/* Honor the user opt-out decision */
+	if (vdev->disable_cxl)
+		return;
+
 	if (!pcie_is_cxl(pdev))
 		return;
 
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 22cf9ea831f9..a6b0fb882b9f 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -60,6 +60,12 @@ static bool disable_denylist;
 module_param(disable_denylist, bool, 0444);
 MODULE_PARM_DESC(disable_denylist, "Disable use of device denylist. Disabling the denylist allows binding to devices with known errata that may lead to exploitable stability or security issues when accessed by untrusted users.");
 
+#if IS_ENABLED(CONFIG_VFIO_CXL_CORE)
+static bool disable_cxl;
+module_param(disable_cxl, bool, 0444);
+MODULE_PARM_DESC(disable_cxl, "Disable CXL Type-2 extensions for all devices bound to vfio-pci. Variant drivers may instead set vdev->disable_cxl in their probe for per-device control without needing this parameter.");
+#endif
+
 static bool vfio_pci_dev_in_denylist(struct pci_dev *pdev)
 {
 	switch (pdev->vendor) {
@@ -189,6 +195,9 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 		return PTR_ERR(vdev);
 
 	dev_set_drvdata(&pdev->dev, vdev);
+#if IS_ENABLED(CONFIG_VFIO_CXL_CORE)
+	vdev->disable_cxl = disable_cxl;
+#endif
 	vdev->pci_ops = &vfio_pci_dev_ops;
 	ret = vfio_pci_core_register_device(vdev);
 	if (ret)
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index aa159d0c8da7..48dc69df52fa 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -130,6 +130,7 @@ struct vfio_pci_core_device {
 	bool			needs_pm_restore:1;
 	bool			pm_intx_masked:1;
 	bool			pm_runtime_engaged:1;
+	bool                    disable_cxl:1;
 	struct pci_saved_state	*pci_saved_state;
 	struct pci_saved_state	*pm_save;
 	int			ioeventfds_nr;
-- 
2.25.1