[PATCH] block: change rq_integrity_vec to respect the iterator

[Anuj gupta]

On Tue, Apr 30, 2024 at 12:07 AM Mikulas Patocka <mpatocka at redhat.com> wrote:
>
> Hi
>
> I am changing dm-crypt, so that it can store the autenticated encryption
> tag directly into the NVMe metadata (without using dm-integrity). This
> will improve performance significantly, because we can avoid journaling
> done by dm-integrity. I've got it working, but I've found this bug, so I'm
> sending a patch for it.
>
> Mikulas
>
>
> From: Mikulas Patocka <mpatocka at redhat.com>
>
> If we allocate a bio that is larger than NVMe maximum request size, attach
> integrity metadata to it and send it to the NVMe subsystem, the integrity
> metadata will be corrupted.
>
> Splitting the bio works correctly. The function bio_split will clone the
> bio, trim the size of the first bio and advance the iterator of the second
> bio.
>
> However, the function rq_integrity_vec has a bug - it returns the first
> vector of the bio's metadata and completely disregards the metadata
> iterator that was advanced when the bio was split. Thus, the second bio
> uses the same metadata as the first bio and this leads to metadata
> corruption.
>
> This commit changes rq_integrity_vec, so that it calls mp_bvec_iter_bvec
> instead of returning the first vector. mp_bvec_iter_bvec reads the
> iterator and advances the vector by the iterator.

We also encountered this issue with split and had a similar solution [1]
This needs a fixes tag too.
fixes <2a876f5e25e8e> ("block: add a rq_integrity_vec helper")

>
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
>
> ---
>  drivers/nvme/host/pci.c       |    6 +++---
>  include/linux/blk-integrity.h |   12 ++++++------
>  2 files changed, 9 insertions(+), 9 deletions(-)
>
> Index: linux-2.6/drivers/nvme/host/pci.c
> ===================================================================
> --- linux-2.6.orig/drivers/nvme/host/pci.c
> +++ linux-2.6/drivers/nvme/host/pci.c
> @@ -825,9 +825,9 @@ static blk_status_t nvme_map_metadata(st
>                 struct nvme_command *cmnd)
>  {
>         struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> +       struct bio_vec bv = rq_integrity_vec(req);
>
> -       iod->meta_dma = dma_map_bvec(dev->dev, rq_integrity_vec(req),
> -                       rq_dma_dir(req), 0);
> +       iod->meta_dma = dma_map_bvec(dev->dev, &bv, rq_dma_dir(req), 0);
>         if (dma_mapping_error(dev->dev, iod->meta_dma))
>                 return BLK_STS_IOERR;
>         cmnd->rw.metadata = cpu_to_le64(iod->meta_dma);
> @@ -966,7 +966,7 @@ static __always_inline void nvme_pci_unm
>                 struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
>
>                 dma_unmap_page(dev->dev, iod->meta_dma,
> -                              rq_integrity_vec(req)->bv_len, rq_dma_dir(req));
> +                              rq_integrity_vec(req).bv_len, rq_dma_dir(req));
>         }
>
>         if (blk_rq_nr_phys_segments(req))
> Index: linux-2.6/include/linux/blk-integrity.h
> ===================================================================
> --- linux-2.6.orig/include/linux/blk-integrity.h
> +++ linux-2.6/include/linux/blk-integrity.h
> @@ -109,11 +109,11 @@ static inline bool blk_integrity_rq(stru
>   * Return the first bvec that contains integrity data.  Only drivers that are
>   * limited to a single integrity segment should use this helper.
>   */

The comment here needs to be updated. rq_integrity_vec now becomes an
iter based operation that can be used by drivers with multiple
integrity segments.

> -static inline struct bio_vec *rq_integrity_vec(struct request *rq)
> +static inline struct bio_vec rq_integrity_vec(struct request *rq)
>  {
> -       if (WARN_ON_ONCE(queue_max_integrity_segments(rq->q) > 1))
> -               return NULL;
> -       return rq->bio->bi_integrity->bip_vec;
> +       WARN_ON_ONCE(queue_max_integrity_segments(rq->q) > 1);
> +       return mp_bvec_iter_bvec(rq->bio->bi_integrity->bip_vec,
> +                                rq->bio->bi_integrity->bip_iter);
>  }
>  #else /* CONFIG_BLK_DEV_INTEGRITY */
>  static inline int blk_rq_count_integrity_sg(struct request_queue *q,
> @@ -177,9 +177,9 @@ static inline int blk_integrity_rq(struc
>         return 0;
>  }
>
> -static inline struct bio_vec *rq_integrity_vec(struct request *rq)
> +static inline struct bio_vec rq_integrity_vec(struct request *rq)
>  {
> -       return NULL;
> +       BUG();
>  }
>  #endif /* CONFIG_BLK_DEV_INTEGRITY */
>  #endif /* _LINUX_BLK_INTEGRITY_H */
>
>
[1] https://lore.kernel.org/linux-block/20240425183943.6319-6-joshi.k@samsung.com/
--
Anuj Gupta