Re: [PATCH v2 3/7] mm/thp: fix vma_address() if virtual address below file offset

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Thu, Jun 03, 2021 at 02:40:30PM -0700, Hugh Dickins wrote:
>  static inline unsigned long
> -__vma_address(struct page *page, struct vm_area_struct *vma)
> +vma_address(struct page *page, struct vm_area_struct *vma)
>  {
> -	pgoff_t pgoff = page_to_pgoff(page);
> -	return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> +	pgoff_t pgoff;
> +	unsigned long address;
> +
> +	VM_BUG_ON_PAGE(PageKsm(page), page);	/* KSM page->index unusable */
> +	pgoff = page_to_pgoff(page);
> +	if (pgoff >= vma->vm_pgoff) {
> +		address = vma->vm_start +
> +			((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> +		/* Check for address beyond vma (or wrapped through 0?) */
> +		if (address < vma->vm_start || address >= vma->vm_end)
> +			address = -EFAULT;
> +	} else if (PageHead(page) &&
> +		   pgoff + compound_nr(page) > vma->vm_pgoff) {

I think on 32-bit, you need ...

		   pgoff + compound_nr(page) - 1 >= vma->vm_pgoff

... right?

> +		address = vma->vm_start;
> +	} else {
> +		address = -EFAULT;
> +	}
> +	return address;
>  }