Hi,
On Thu, Jun 20, 2019 at 02:02:21PM +0800, Herbert Xu wrote:
> 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.
could you explain how sg->offset becomes >= PAGE_SIZE?
--Imre
> > 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/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
