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Subject[PATCH v3 2/2] Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio"
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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>
---
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 77e64e3eac80..8c3729eb3e38 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
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