[PATCH 4/5] vfio: Introduce vfio_device_ops.get_unmapped_area hook

Peter Xu
2025-06-13T13:41:30Z

Add a hook to vfio_device_ops to allow sub-modules provide virtual
addresses for an mmap() request.

Note that the fallback will be mm_get_unmapped_area(), which should
maintain the old behavior of generic VA allocation (__get_unmapped_area).
It's a bit unfortunate that is needed, as the current get_unmapped_area()
file ops cannot support a retval which fallbacks to the default. So that
is needed both here and whenever sub-module will opt-in with its own.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
drivers/vfio/vfio_main.c | 18 ++++++++++++++++++
include/linux/vfio.h | 7 +++++++
2 files changed, 25 insertions(+)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 1fd261efc582..19db8e58d223 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -1354,6 +1354,23 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma)
return device->ops->mmap(device, vma);
}

+static unsigned long vfio_device_get_unmapped_area(struct file *file,
+ unsigned long addr,
+ unsigned long len,
+ unsigned long pgoff,
+ unsigned long flags)
+{
+ struct vfio_device_file *df = file->private_data;
+ struct vfio_device *device = df->device;
+
+ if (!device->ops->get_unmapped_area)
+ return mm_get_unmapped_area(current->mm, file, addr,
+ len, pgoff, flags);
+
+ return device->ops->get_unmapped_area(device, file, addr, len,
+ pgoff, flags);
+}
+
const struct file_operations vfio_device_fops = {
.owner = THIS_MODULE,
.open = vfio_device_fops_cdev_open,
@@ -1363,6 +1380,7 @@ const struct file_operations vfio_device_fops = {
.unlocked_ioctl = vfio_device_fops_unl_ioctl,
.compat_ioctl = compat_ptr_ioctl,
.mmap = vfio_device_fops_mmap,
+ .get_unmapped_area = vfio_device_get_unmapped_area,
};

static struct vfio_device *vfio_device_from_file(struct file *file)
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 707b00772ce1..48fe71c61ed2 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -108,6 +108,7 @@ struct vfio_device {
* @dma_unmap: Called when userspace unmaps IOVA from the container
* this device is attached to.
* @device_feature: Optional, fill in the VFIO_DEVICE_FEATURE ioctl
+ * @get_unmapped_area: Optional, provide virtual address hint for mmap()
*/
struct vfio_device_ops {
char *name;
@@ -135,6 +136,12 @@ struct vfio_device_ops {
void (*dma_unmap)(struct vfio_device *vdev, u64 iova, u64 length);
int (*device_feature)(struct vfio_device *device, u32 flags,
void __user *arg, size_t argsz);
+ unsigned long (*get_unmapped_area)(struct vfio_device *device,
+ struct file *file,
+ unsigned long addr,
+ unsigned long len,
+ unsigned long pgoff,
+ unsigned long flags);
};

#if IS_ENABLED(CONFIG_IOMMUFD)
--
2.49.0