On Thu, Apr 18, 2019 at 11:36:03AM +0200, Paolo Bonzini wrote: > On 18/04/19 11:29, Ming Lei wrote: > > 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: > > Uff, I can't read apparently. :( This is the commit that introduced it: > > commit 4d6af73d9e43f78651a43ee4c5ad221107ac8365 > Author: Christoph Hellwig <hch@xxxxxx> > Date: Wed Mar 2 18:07:14 2016 +0100 > > block: support large requests in blk_rq_map_user_iov Exactly, the above commit starts to build multiple bios for a request. Then I guess your issue is triggered on kernel without the commit. Thanks, Ming
