Re: [PATCH v2 06/28] gup: Fix some contiguous memmap assumptions

[Christoph Hellwig]

On Mon, Jan 10, 2022 at 04:23:44AM +0000, Matthew Wilcox (Oracle) wrote:
> Several functions in gup.c assume that a compound page has virtually
> contiguous page structs.  This isn't true for SPARSEMEM configs unless
> SPARSEMEM_VMEMMAP is also set.  Fix them by using nth_page() instead of
> plain pointer arithmetic.

So is this an actualy bug that need a Fixes tag, or do all architectures
that support THP and sparsemem use SPARSEMEM_VMEMMAP?

> +	page = nth_page(head, (addr & (sz-1)) >> PAGE_SHIFT);

Would be nice to fix the indeation for sz - 1 while you're at it.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@xxxxxx>