linux-kernel - [PATCH 4/5] vfio: Introduce vfio_device_ops.get_unmapped

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Message-ID: <20250613134111.469884-5-peterx@redhat.com>
Date: Fri, 13 Jun 2025 09:41:10 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	kvm@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Zi Yan <ziy@...dia.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Alex Mastro <amastro@...com>,
	David Hildenbrand <david@...hat.com>,
	Nico Pache <npache@...hat.com>,
	peterx@...hat.com
Subject: [PATCH 4/5] vfio: Introduce vfio_device_ops.get_unmapped_area hook

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@...hat.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