On Mon, Jun 17, 2019 at 09:15:02PM +0000, Christophe Leroy wrote:
> All mapping iterator logic is based on the assumption that sg->offset
> is always lower than PAGE_SIZE.
>
> But there are situations where sg->offset is such that the SG item
> is on the second page. In that case sg_copy_to_buffer() fails
> properly copying the data into the buffer. One of the reason is
> that the data will be outside the kmapped area used to access that
> data.
>
> This patch fixes the issue by adjusting the mapping iterator
> offset and pgoffset fields such that offset is always lower than
> PAGE_SIZE.
>
> Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
> Fixes: 4225fc8555a9 ("lib/scatterlist: use page iterator in the mapping
> iterator")
> Cc: sta...@vger.kernel.org
> ---
> lib/scatterlist.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
Good catch.
> @@ -686,7 +686,12 @@ static bool sg_miter_get_next_page(struct
> sg_mapping_iter *miter)
> sg = miter->piter.sg;
> pgoffset = miter->piter.sg_pgoffset;
>
> - miter->__offset = pgoffset ? 0 : sg->offset;
> + offset = pgoffset ? 0 : sg->offset;
> + while (offset >= PAGE_SIZE) {
> + miter->piter.sg_pgoffset = ++pgoffset;
> + offset -= PAGE_SIZE;
> + }
How about
miter->piter.sg_pgoffset += offset >> PAGE_SHIFT;
offset &= PAGE_SIZE - 1;
Thanks,
--
Email: Herbert Xu <herb...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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