vfio: Move iova_bitmap into iommufd

Both VFIO and IOMMUFD will need iova bitmap for storing dirties and walking
the user bitmaps, so move to the common dependency into IOMMUFD.  In doing
so, create the symbol IOMMUFD_DRIVER which designates the builtin code that
will be used by drivers when selected. Today this means MLX5_VFIO_PCI and
PDS_VFIO_PCI. IOMMU drivers will do the same (in future patches) when
supporting dirty tracking and select IOMMUFD_DRIVER accordingly.

Given that the symbol maybe be disabled, add header definitions in
iova_bitmap.h for when IOMMUFD_DRIVER=n

Link: https://lore.kernel.org/r/20231024135109.73787-3-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/Kconfig

@@ -7,6 +7,10 @@ config IOMMU_IOVA
 config IOMMU_API
 	bool
 
+config IOMMUFD_DRIVER
+	bool
+	default n
+
 menuconfig IOMMU_SUPPORT
 	bool "IOMMU Hardware Support"
 	depends on MMU

drivers/iommu/iommufd/Makefile

@@ -11,3 +11,4 @@ iommufd-y := \
 iommufd-$(CONFIG_IOMMUFD_TEST) += selftest.o
 
 obj-$(CONFIG_IOMMUFD) += iommufd.o
+obj-$(CONFIG_IOMMUFD_DRIVER) += iova_bitmap.o

drivers/vfio/Makefile

@@ -1,8 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_VFIO) += vfio.o
 
-vfio-y += vfio_main.o \
-	  iova_bitmap.o
+vfio-y += vfio_main.o
 vfio-$(CONFIG_VFIO_DEVICE_CDEV) += device_cdev.o
 vfio-$(CONFIG_VFIO_GROUP) += group.o
 vfio-$(CONFIG_IOMMUFD) += iommufd.o

drivers/vfio/pci/mlx5/Kconfig

@@ -3,6 +3,7 @@ config MLX5_VFIO_PCI
 	tristate "VFIO support for MLX5 PCI devices"
 	depends on MLX5_CORE
 	select VFIO_PCI_CORE
+	select IOMMUFD_DRIVER
 	help
 	  This provides migration support for MLX5 devices using the VFIO
 	  framework.

drivers/vfio/pci/pds/Kconfig

@@ -5,6 +5,7 @@ config PDS_VFIO_PCI
 	tristate "VFIO support for PDS PCI devices"
 	depends on PDS_CORE
 	select VFIO_PCI_CORE
+	select IOMMUFD_DRIVER
 	help
 	  This provides generic PCI support for PDS devices using the VFIO
 	  framework.

include/linux/iova_bitmap.h

@@ -7,6 +7,7 @@
 #define _IOVA_BITMAP_H_
 
 #include <linux/types.h>
+#include <linux/errno.h>
 
 struct iova_bitmap;
 
@@ -14,6 +15,7 @@ typedef int (*iova_bitmap_fn_t)(struct iova_bitmap *bitmap,
 				unsigned long iova, size_t length,
 				void *opaque);
 
+#if IS_ENABLED(CONFIG_IOMMUFD_DRIVER)
 struct iova_bitmap *iova_bitmap_alloc(unsigned long iova, size_t length,
 				      unsigned long page_size,
 				      u64 __user *data);
@@ -22,5 +24,29 @@ int iova_bitmap_for_each(struct iova_bitmap *bitmap, void *opaque,
 			 iova_bitmap_fn_t fn);
 void iova_bitmap_set(struct iova_bitmap *bitmap,
 		     unsigned long iova, size_t length);
+#else
+static inline struct iova_bitmap *iova_bitmap_alloc(unsigned long iova,
+						    size_t length,
+						    unsigned long page_size,
+						    u64 __user *data)
+{
+	return NULL;
+}
+
+static inline void iova_bitmap_free(struct iova_bitmap *bitmap)
+{
+}
+
+static inline int iova_bitmap_for_each(struct iova_bitmap *bitmap, void *opaque,
+				       iova_bitmap_fn_t fn)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void iova_bitmap_set(struct iova_bitmap *bitmap,
+				   unsigned long iova, size_t length)
+{
+}
+#endif
 
 #endif