On Thu, 13 May 2021, Bart Van Assche wrote:
> On 5/13/21 12:22 PM, Mikulas Patocka wrote:
> > We already had problems with too large bios in dm-crypt and we fixed it by
> > adding this piece of code:
> >
> > /*
> > * Check if bio is too large, split as needed.
> > */
> > if (unlikely(bio->bi_iter.bi_size > (BIO_MAX_VECS << PAGE_SHIFT)) &&
> > (bio_data_dir(bio) == WRITE || cc->on_disk_tag_size))
> > dm_accept_partial_bio(bio, ((BIO_MAX_VECS << PAGE_SHIFT) >> SECTOR_SHIFT));
> >
> > It will ask the device mapper to split the bio if it is too large. So,
> > crypt_alloc_buffer can't receive a bio that is larger than BIO_MAX_VECS <<
> > PAGE_SHIFT.
>
> Hi Mikulas,
>
> Are you perhaps referring to commit 4e870e948fba ("dm crypt: fix error
> with too large bios")? Did that commit go upstream before multi-page
> bvec support?
Yes. It's from 2016.
> Can larger bios be supported in case of two or more
> contiguous pages now that multi-page bvec support is upstream?
No - we need to allocate a buffer for the written data. The buffer size is
limited to PAGE_SIZE * BIO_MAX_VECS.
> Thanks,
>
> Bart.
Mikulas
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