[PATCH v4 2/3] Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio"

[Brian Geffon <bgeffon@google.com>]

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 -EFAULT.

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

Signed-off-by: Brian Geffon <bgeffon@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
---
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 2 +-
 fs/aio.c                                  | 5 +----
 include/linux/mm.h                        | 2 +-
 mm/mmap.c                                 | 6 +-----
 mm/mremap.c                               | 2 +-
 5 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index e916646adc69..0daf2f1cf7a8 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -1458,7 +1458,7 @@ static int pseudo_lock_dev_release(struct inode *inode, struct file *filp)
 	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;
diff --git a/fs/aio.c b/fs/aio.c
index 1f32da13d39e..76ce0cc3ee4e 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -323,16 +323,13 @@ static void aio_free_ring(struct kioctx *ctx)
 	}
 }
 
-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();
 	table = rcu_dereference(mm->ioctx_table);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 64a71bf20536..ecdc6e8dc5af 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -570,7 +570,7 @@ struct vm_operations_struct {
 	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
diff --git a/mm/mmap.c b/mm/mmap.c
index 3f287599a7a3..9d7651e4e1fe 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3403,14 +3403,10 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
 	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;
 
diff --git a/mm/mremap.c b/mm/mremap.c
index db5b8b28c2dd..d22629ff8f3c 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -545,7 +545,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	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)) {
-- 
2.31.0.rc2.261.g7f71774620-goog