[PATCH v4 19/21] uio: replace deprecated mmap hook with mmap_prepare in uio_info

["Lorenzo Stoakes (Oracle)" <ljs@kernel.org>]

The f_op->mmap interface is deprecated, so update uio_info to use its
successor, mmap_prepare.

Therefore, replace the uio_info->mmap hook with a new
uio_info->mmap_prepare hook, and update its one user, target_core_user,
to both specify this new mmap_prepare hook and also to use the new
vm_ops->mapped() hook to continue to maintain a correct udev->kref
refcount.

Then update uio_mmap() to utilise the mmap_prepare compatibility layer to
invoke this callback from the uio mmap invocation.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/target/target_core_user.c | 26 ++++++++++++++++++--------
 drivers/uio/uio.c                 | 10 ++++++++--
 include/linux/uio_driver.h        |  4 ++--
 3 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index af95531ddd35..edc2afd5f4ee 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1860,6 +1860,17 @@ static struct page *tcmu_try_get_data_page(struct tcmu_dev *udev, uint32_t dpi)
 	return NULL;
 }
 
+static int tcmu_vma_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
+			   const struct file *file, void **vm_private_data)
+{
+	struct tcmu_dev *udev = *vm_private_data;
+
+	pr_debug("vma_mapped\n");
+
+	kref_get(&udev->kref);
+	return 0;
+}
+
 static void tcmu_vma_open(struct vm_area_struct *vma)
 {
 	struct tcmu_dev *udev = vma->vm_private_data;
@@ -1919,26 +1930,25 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
 }
 
 static const struct vm_operations_struct tcmu_vm_ops = {
+	.mapped = tcmu_vma_mapped,
 	.open = tcmu_vma_open,
 	.close = tcmu_vma_close,
 	.fault = tcmu_vma_fault,
 };
 
-static int tcmu_mmap(struct uio_info *info, struct vm_area_struct *vma)
+static int tcmu_mmap_prepare(struct uio_info *info, struct vm_area_desc *desc)
 {
 	struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info);
 
-	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP);
-	vma->vm_ops = &tcmu_vm_ops;
+	vma_desc_set_flags(desc, VMA_DONTEXPAND_BIT, VMA_DONTDUMP_BIT);
+	desc->vm_ops = &tcmu_vm_ops;
 
-	vma->vm_private_data = udev;
+	desc->private_data = udev;
 
 	/* Ensure the mmap is exactly the right size */
-	if (vma_pages(vma) != udev->mmap_pages)
+	if (vma_desc_pages(desc) != udev->mmap_pages)
 		return -EINVAL;
 
-	tcmu_vma_open(vma);
-
 	return 0;
 }
 
@@ -2253,7 +2263,7 @@ static int tcmu_configure_device(struct se_device *dev)
 	info->irqcontrol = tcmu_irqcontrol;
 	info->irq = UIO_IRQ_CUSTOM;
 
-	info->mmap = tcmu_mmap;
+	info->mmap_prepare = tcmu_mmap_prepare;
 	info->open = tcmu_open;
 	info->release = tcmu_release;
 
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 5a4998e2caf8..1e4ade78ed84 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -850,8 +850,14 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 		goto out;
 	}
 
-	if (idev->info->mmap) {
-		ret = idev->info->mmap(idev->info, vma);
+	if (idev->info->mmap_prepare) {
+		struct vm_area_desc desc;
+
+		compat_set_desc_from_vma(&desc, filep, vma);
+		ret = idev->info->mmap_prepare(idev->info, &desc);
+		if (ret)
+			goto out;
+		ret = __compat_vma_mmap(&desc, vma);
 		goto out;
 	}
 
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 334641e20fb1..02eaac47ac44 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -97,7 +97,7 @@ struct uio_device {
  * @irq_flags:		flags for request_irq()
  * @priv:		optional private data
  * @handler:		the device's irq handler
- * @mmap:		mmap operation for this uio device
+ * @mmap_prepare:	mmap_prepare operation for this uio device
  * @open:		open operation for this uio device
  * @release:		release operation for this uio device
  * @irqcontrol:		disable/enable irqs when 0/1 is written to /dev/uioX
@@ -112,7 +112,7 @@ struct uio_info {
 	unsigned long		irq_flags;
 	void			*priv;
 	irqreturn_t (*handler)(int irq, struct uio_info *dev_info);
-	int (*mmap)(struct uio_info *info, struct vm_area_struct *vma);
+	int (*mmap_prepare)(struct uio_info *info, struct vm_area_desc *desc);
 	int (*open)(struct uio_info *info, struct inode *inode);
 	int (*release)(struct uio_info *info, struct inode *inode);
 	int (*irqcontrol)(struct uio_info *info, s32 irq_on);
-- 
2.53.0