On Thu, Apr 18, 2019 at 10:42:21AM +0200, Paolo Bonzini wrote:
On 18/04/19 04:19, Ming Lei wrote:
Hi Paolo,
On Wed, Apr 17, 2019 at 01:52:07PM +0200, Paolo Bonzini wrote:
Because bio_kmalloc uses inline iovecs, the limit on the number of entries is not BIO_MAX_PAGES but rather UIO_MAXIOV, which indeed is already checked in bio_kmalloc. This could cause SG_IO requests to be truncated and the HBA to report a DMA overrun.
BIO_MAX_PAGES only limits the single bio's max vector number, if one bio can't hold all user space request, new bio will be allocated and appended to the passthrough request if queue limits aren't reached.
Stupid question: where? I don't see any place starting at blk_rq_map_user_iov (and then __blk_rq_map_user_iov->bio_map_user_iov) that would allocate a second bio. The only bio_kmalloc in that path is the one I'm patching.
Each bio is created inside __blk_rq_map_user_iov() which is run inside a loop, and the created bio is added to request via blk_rq_append_bio(), see the following code:
blk_rq_map_user_iov __blk_rq_map_user_iov blk_rq_append_bio
blk_rq_map_user_iov(): ... do { ret =__blk_rq_map_user_iov(rq, map_data, &i, gfp_mask, copy); if (ret) goto unmap_rq; if (!bio) bio = rq->bio; } while (iov_iter_count(&i)); ...
Thanks, Ming