[RFC PATCH v2 2/3] mm: secretmem: convert to .mmap_prepare() hook

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Secretmem has a simple .mmap() hook which is easily converted to the new
.mmap_prepare() callback.

Importantly, it's a rare instance of an driver that manipulates a VMA which
is mergeable (that is, not a VM_SPECIAL mapping) while also adjusting VMA
flags which may adjust mergeability, meaning the retry merge logic might
impact whether or not the VMA is merged.

By using .mmap_prepare() there's no longer any need to retry the merge
later as we can simply set the correct flags from the start.

This change therefore allows us to remove the retry merge logic in a
subsequent commit.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 mm/secretmem.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/secretmem.c b/mm/secretmem.c
index 1b0a214ee558..f98cf3654974 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -120,18 +120,18 @@ static int secretmem_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
-static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
+static int secretmem_mmap_prepare(struct vm_area_desc *desc)
 {
-	unsigned long len = vma->vm_end - vma->vm_start;
+	unsigned long len = desc->end - desc->start;
 
-	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
+	if ((desc->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
 		return -EINVAL;
 
-	if (!mlock_future_ok(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
+	if (!mlock_future_ok(desc->mm, desc->vm_flags | VM_LOCKED, len))
 		return -EAGAIN;
 
-	vm_flags_set(vma, VM_LOCKED | VM_DONTDUMP);
-	vma->vm_ops = &secretmem_vm_ops;
+	desc->vm_flags |= VM_LOCKED | VM_DONTDUMP;
+	desc->vm_ops = &secretmem_vm_ops;
 
 	return 0;
 }
@@ -143,7 +143,7 @@ bool vma_is_secretmem(struct vm_area_struct *vma)
 
 static const struct file_operations secretmem_fops = {
 	.release	= secretmem_release,
-	.mmap		= secretmem_mmap,
+	.mmap_prepare	= secretmem_mmap_prepare,
 };
 
 static int secretmem_migrate_folio(struct address_space *mapping,
-- 
2.49.0