Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio"

This reverts commit cd544fd1dc9293c6702fab6effa63dac1cc67e99.

As discussed in [1] this commit was a no-op because the mapping type was
checked in vma_to_resize before move_vma is ever called. This meant that
vm_ops->mremap() would never be called on such mappings. Furthermore,
we've since expanded support of MREMAP_DONTUNMAP to non-anonymous
mappings, and these special mappings are still protected by the existing
check of !VM_DONTEXPAND and !VM_PFNMAP which will result in a -EINVAL.

1. https://lkml.org/lkml/2020/12/28/2340

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Brian Geffon <[e-mail]>
Acked-by: Hugh Dickins <[e-mail]>
Reviewed-by: Dmitry Safonov <[e-mail]>
Cc: Alejandro Colomar <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Axel Rasmussen <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Lokesh Gidra <[e-mail]>
Cc: Michael Kerrisk <[e-mail]>
Cc: "Michael S . Tsirkin" <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Sonny Rao <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/x86/kernel/cpu/resctrl/pseudo_lock.c

···
 	return 0;
 }
 
-static int pseudo_lock_dev_mremap(struct vm_area_struct *area, unsigned long flags)
+static int pseudo_lock_dev_mremap(struct vm_area_struct *area)
 {
 	/* Not supported */
 	return -EINVAL;

fs/aio.c

···
 	}
 }
 
-static int aio_ring_mremap(struct vm_area_struct *vma, unsigned long flags)
+static int aio_ring_mremap(struct vm_area_struct *vma)
 {
 	struct file *file = vma->vm_file;
 	struct mm_struct *mm = vma->vm_mm;
 	struct kioctx_table *table;
 	int i, res = -EINVAL;
-
-	if (flags & MREMAP_DONTUNMAP)
-		return -EINVAL;
 
 	spin_lock(&mm->ioctx_lock);
 	rcu_read_lock();

include/linux/mm.h

···
 	void (*close)(struct vm_area_struct * area);
 	/* Called any time before splitting to check if it's allowed */
 	int (*may_split)(struct vm_area_struct *area, unsigned long addr);
-	int (*mremap)(struct vm_area_struct *area, unsigned long flags);
+	int (*mremap)(struct vm_area_struct *area);
 	/*
 	 * Called by mprotect() to make driver-specific permission
 	 * checks before mprotect() is finalised.   The VMA must not

mm/mmap.c

···
 	return ((struct vm_special_mapping *)vma->vm_private_data)->name;
 }
 
-static int special_mapping_mremap(struct vm_area_struct *new_vma,
-				  unsigned long flags)
+static int special_mapping_mremap(struct vm_area_struct *new_vma)
 {
 	struct vm_special_mapping *sm = new_vma->vm_private_data;
-
-	if (flags & MREMAP_DONTUNMAP)
-		return -EINVAL;
 
 	if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
 		return -EFAULT;

mm/mremap.c

···
 	if (moved_len < old_len) {
 		err = -ENOMEM;
 	} else if (vma->vm_ops && vma->vm_ops->mremap) {
-		err = vma->vm_ops->mremap(new_vma, flags);
+		err = vma->vm_ops->mremap(new_vma);
 	}
 
 	if (unlikely(err)) {