On Fri, Oct 18, 2024 at 01:41:13PM -0400, Liam R. Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
>
> vma_to_resize() is used in two locations to find and validate the vma
> for the mremap location. One of the two locations already has the vma,
> which is then re-found to validate the same vma.
>
> This code can be simplified by moving the vma_lookup() from
> vma_to_resize() to mremap_to() and changing the return type to an int
> error.
>
> Since the function now just validates the vma, the function is renamed
> to resize_is_valid() to better reflect what it is doing.
>
> This commit also adds documentation about the function.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
git-icdiff helped here a lot :)
This LGTM,
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Generally a really nice clean up in any case, thanks for doing this!
> ---
> mm/mremap.c | 53 +++++++++++++++++++++++++++++++----------------------
> 1 file changed, 31 insertions(+), 22 deletions(-)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 5917feafe8cc..e781ec4573ca 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -826,17 +826,24 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> return new_addr;
> }
>
> -static struct vm_area_struct *vma_to_resize(unsigned long addr,
> +/*
> + * resize_is_valid() - Ensure the vma can be resized to the new length at the give
> + * address.
> + *
> + * @vma: The vma to resize
> + * @addr: The old address
> + * @old_len: The current size
> + * @new_len: The desired size
> + * @flags: The vma flags
> + *
> + * Return 0 on success, error otherwise.
> + */
> +static int resize_is_valid(struct vm_area_struct *vma, unsigned long addr,
> unsigned long old_len, unsigned long new_len, unsigned long flags)
> {
> struct mm_struct *mm = current->mm;
> - struct vm_area_struct *vma;
> unsigned long pgoff;
>
> - vma = vma_lookup(mm, addr);
> - if (!vma)
> - return ERR_PTR(-EFAULT);
> -
> /*
> * !old_len is a special case where an attempt is made to 'duplicate'
> * a mapping. This makes no sense for private mappings as it will
> @@ -847,37 +854,37 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> */
> if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
> pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap. This is not supported.\n", current->comm, current->pid);
> - return ERR_PTR(-EINVAL);
> + return -EINVAL;
> }
>
> if ((flags & MREMAP_DONTUNMAP) &&
> (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))
> - return ERR_PTR(-EINVAL);
> + return -EINVAL;
>
> /* We can't remap across vm area boundaries */
> if (old_len > vma->vm_end - addr)
> - return ERR_PTR(-EFAULT);
> + return -EFAULT;
>
> if (new_len == old_len)
> - return vma;
> + return 0;
>
> /* Need to be careful about a growing mapping */
> pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
> pgoff += vma->vm_pgoff;
> if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
> - return ERR_PTR(-EINVAL);
> + return -EINVAL;
>
> if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
> - return ERR_PTR(-EFAULT);
> + return -EFAULT;
>
> if (!mlock_future_ok(mm, vma->vm_flags, new_len - old_len))
> - return ERR_PTR(-EAGAIN);
> + return -EAGAIN;
>
> if (!may_expand_vm(mm, vma->vm_flags,
> (new_len - old_len) >> PAGE_SHIFT))
> - return ERR_PTR(-ENOMEM);
> + return -ENOMEM;
>
> - return vma;
> + return 0;
> }
>
> static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> @@ -936,12 +943,16 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> old_len = new_len;
> }
>
> - vma = vma_to_resize(addr, old_len, new_len, flags);
> - if (IS_ERR(vma)) {
> - ret = PTR_ERR(vma);
> + vma = vma_lookup(mm, addr);
> + if (!vma) {
> + ret = -EFAULT;
> goto out;
> }
>
> + ret = resize_is_valid(vma, addr, old_len, new_len, flags);
> + if (ret)
> + goto out;
> +
> /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
> if (flags & MREMAP_DONTUNMAP &&
> !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
> @@ -1114,11 +1125,9 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> /*
> * Ok, we need to grow..
> */
> - vma = vma_to_resize(addr, old_len, new_len, flags);
> - if (IS_ERR(vma)) {
> - ret = PTR_ERR(vma);
> + ret = resize_is_valid(vma, addr, old_len, new_len, flags);
> + if (ret)
> goto out;
> - }
>
> /* old_len exactly to the end of the area..
> */
> --
> 2.43.0
>
