[PATCH v5 14/27] vfio/pci: Provide an opt-out for the CXL Type-2 extensions

[<mhonap@nvidia.com>]

From: Manish Honap <mhonap@nvidia.com>

Let an admin or a variant driver keep the CXL Type-2 extensions out of
the path and drive the device as plain vfio-pci. Add a
vfio_pci.disable_cxl module parameter, and let a variant driver set
vdev->disable_cxl in its own init callback for per-device control. The
parameter is built only when the CXL provider is configured.

Assisted-by: LLM
Signed-off-by: Manish Honap <mhonap@nvidia.com>
---
 drivers/vfio/pci/vfio_pci.c   | 13 +++++++++++++
 include/linux/vfio_pci_core.h |  1 +
 2 files changed, 14 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 830369ff878d..66f2e318d8e5 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -60,6 +60,16 @@ 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)
+/*
+ * A variant driver may instead set vdev->disable_cxl in its own init callback
+ * for per-device control without this module-wide parameter.
+ */
+static bool disable_cxl;
+module_param(disable_cxl, bool, 0644);
+MODULE_PARM_DESC(disable_cxl, "Disable CXL Type-2 extensions for all devices bound to vfio-pci.");
+#endif
+
 static bool vfio_pci_dev_in_denylist(struct pci_dev *pdev)
 {
 	switch (pdev->vendor) {
@@ -142,6 +152,9 @@ static int vfio_pci_init_dev(struct vfio_device *core_vdev)
 #ifdef CONFIG_VFIO_PCI_VGA
 	vdev->disable_vga = disable_vga;
 #endif
+#if IS_ENABLED(CONFIG_VFIO_CXL)
+	vdev->disable_cxl = disable_cxl;
+#endif
 
 	return vfio_pci_core_init_dev(core_vdev);
 }
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 6ebf9a26275e..475a0ecf9e4f 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -149,6 +149,7 @@ struct vfio_pci_core_device {
 	bool			disable_idle_d3:1;
 	bool			nointxmask:1;
 	bool			disable_vga:1;
+	bool			disable_cxl:1;
 	/* Flags modified at runtime - dedicated storage unit */
 	bool			needs_reset;
 	bool			pm_intx_masked;
-- 
2.25.1