[PATCH v6 18/31] vfio/cxl: Add the vfio-cxl provider module skeleton

[<mhonap@nvidia.com>]

From: Manish Honap <mhonap@nvidia.com>

Add the vfio-cxl module that vfio-pci-core loads on demand for a CXL
Type-2 device, registering its callbacks at module_init. Its reset op
runs the PCI core's reset methods until vfio-cxl serves the device
memory.

vfio-cxl is a feature of vfio-pci-core rather than a variant driver, so
its Kconfig sources above the variant drivers and its objects link right
after vfio-pci-core while still being loaded on demand:
request_module("vfio-cxl") finds it by module name.

Assisted-by: LLM
Signed-off-by: Manish Honap <mhonap@nvidia.com>
---
 MAINTAINERS                          |  7 +++
 drivers/vfio/pci/Kconfig             |  2 +
 drivers/vfio/pci/Makefile            |  2 +
 drivers/vfio/pci/cxl/Kconfig         | 11 ++++
 drivers/vfio/pci/cxl/Makefile        |  3 +
 drivers/vfio/pci/cxl/vfio_cxl_core.c | 82 ++++++++++++++++++++++++++++
 6 files changed, 107 insertions(+)
 create mode 100644 drivers/vfio/pci/cxl/Kconfig
 create mode 100644 drivers/vfio/pci/cxl/Makefile
 create mode 100644 drivers/vfio/pci/cxl/vfio_cxl_core.c

diff --git a/MAINTAINERS b/MAINTAINERS
index c3aef3dce68c..8ac0a91ce647 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -28636,6 +28636,13 @@ L:	kvm@vger.kernel.org
 S:	Maintained
 F:	drivers/vfio/cdx/*
 
+VFIO CXL DRIVER
+M:	Manish Honap <mhonap@nvidia.com>
+L:	kvm@vger.kernel.org
+L:	linux-cxl@vger.kernel.org
+S:	Supported
+F:	drivers/vfio/pci/cxl/
+
 VFIO DRIVER
 M:	Alex Williamson <alex@shazbot.org>
 L:	kvm@vger.kernel.org
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index 296bf01e185e..4cd6acd36053 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -58,6 +58,8 @@ config VFIO_PCI_ZDEV_KVM
 config VFIO_PCI_DMABUF
 	def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER
 
+source "drivers/vfio/pci/cxl/Kconfig"
+
 source "drivers/vfio/pci/mlx5/Kconfig"
 
 source "drivers/vfio/pci/ism/Kconfig"
diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index 6138f1bf241d..b65117d8d463 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -5,6 +5,8 @@ vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
 vfio-pci-core-$(CONFIG_VFIO_PCI_DMABUF) += vfio_pci_dmabuf.o
 obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
 
+obj-$(CONFIG_VFIO_CXL) += cxl/
+
 vfio-pci-y := vfio_pci.o
 vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
 obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
diff --git a/drivers/vfio/pci/cxl/Kconfig b/drivers/vfio/pci/cxl/Kconfig
new file mode 100644
index 000000000000..1392fa4ed15d
--- /dev/null
+++ b/drivers/vfio/pci/cxl/Kconfig
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config VFIO_CXL
+	tristate "VFIO support for CXL Type-2 devices"
+	depends on CXL_BUS && CXL_MEM
+	select VFIO_PCI_CORE
+	help
+	  Add CXL HDM handling to vfio-pci so a CXL Type-2 device, such as a
+	  CXL-attached accelerator, can be assigned to a virtual machine.
+	  vfio-pci loads this module on demand when it binds a CXL device.
+
+	  If you don't know what to do here, say N.
diff --git a/drivers/vfio/pci/cxl/Makefile b/drivers/vfio/pci/cxl/Makefile
new file mode 100644
index 000000000000..8501bf626108
--- /dev/null
+++ b/drivers/vfio/pci/cxl/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_VFIO_CXL) += vfio-cxl.o
+vfio-cxl-y := vfio_cxl_core.o
diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c b/drivers/vfio/pci/cxl/vfio_cxl_core.c
new file mode 100644
index 000000000000..ee49d68d689c
--- /dev/null
+++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * VFIO support for CXL Type-2 devices.
+ *
+ * Copyright (c) 2026 NVIDIA Corporation & Affiliates
+ */
+
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/vfio_pci_core.h>
+
+static int vfio_cxl_init_device(struct vfio_pci_core_device *vdev)
+{
+	return 0;
+}
+
+static void vfio_cxl_release_device(struct vfio_pci_core_device *vdev)
+{
+}
+
+static int vfio_cxl_open_device(struct vfio_pci_core_device *vdev)
+{
+	return 0;
+}
+
+static void vfio_cxl_close_device(struct vfio_pci_core_device *vdev)
+{
+}
+
+static void vfio_cxl_reset_prepare(struct vfio_pci_core_device *vdev)
+{
+}
+
+static int vfio_cxl_reset_done(struct vfio_pci_core_device *vdev)
+{
+	return 0;
+}
+
+/*
+ * Until vfio-cxl serves the device memory, reset through the PCI core's
+ * reset methods, which run CXL Reset ahead of FLR. Restore the PCI state
+ * here rather than through pci_reset_function_locked(): its reset_prepare
+ * and reset_done callbacks take memory_lock, which the caller already holds.
+ * The caller has saved the state, or on close loaded the open-time copy.
+ */
+static int vfio_cxl_reset(struct vfio_pci_core_device *vdev)
+{
+	struct pci_dev *pdev = vdev->pdev;
+	int ret;
+
+	ret = __pci_reset_function_locked(pdev);
+	pci_restore_state(pdev);
+
+	return ret;
+}
+
+static const struct vfio_cxl_ops vfio_cxl_ops = {
+	.init		= vfio_cxl_init_device,
+	.release	= vfio_cxl_release_device,
+	.open_device	= vfio_cxl_open_device,
+	.close_device	= vfio_cxl_close_device,
+	.reset_prepare	= vfio_cxl_reset_prepare,
+	.reset_done	= vfio_cxl_reset_done,
+	.reset		= vfio_cxl_reset,
+	.owner		= THIS_MODULE,
+};
+
+static int __init vfio_cxl_init(void)
+{
+	return vfio_pci_core_register_cxl_ops(&vfio_cxl_ops);
+}
+
+static void __exit vfio_cxl_exit(void)
+{
+	vfio_pci_core_unregister_cxl_ops(&vfio_cxl_ops);
+}
+
+module_init(vfio_cxl_init);
+module_exit(vfio_cxl_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("VFIO support for CXL Type-2 devices");
-- 
2.53.0