> Subject: Re: [PATCH for-rc 1/3] RDMA/core: Fix umem iterator when PAGE_SIZE
> is greater then HCA pgsz
>
> On Wed, Nov 15, 2023 at 01:17:50PM -0600, Shiraz Saleem wrote:
> > diff --git a/drivers/infiniband/core/umem.c
> > b/drivers/infiniband/core/umem.c index f9ab671c8eda..07c571c7b699
> > 100644
> > --- a/drivers/infiniband/core/umem.c
> > +++ b/drivers/infiniband/core/umem.c
> > @@ -96,12 +96,6 @@ unsigned long ib_umem_find_best_pgsz(struct
> ib_umem *umem,
> > return page_size;
> > }
> >
> > - /* rdma_for_each_block() has a bug if the page size is smaller than the
> > - * page size used to build the umem. For now prevent smaller page sizes
> > - * from being returned.
> > - */
> > - pgsz_bitmap &= GENMASK(BITS_PER_LONG - 1, PAGE_SHIFT);
> > -
> > /* The best result is the smallest page size that results in the minimum
> > * number of required pages. Compute the largest page size that could
> > * work based on VA address bits that don't change.
> > diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h index
> > 95896472a82b..e775d1b4910c 100644
> > --- a/include/rdma/ib_umem.h
> > +++ b/include/rdma/ib_umem.h
> > @@ -77,6 +77,8 @@ static inline void
> > __rdma_umem_block_iter_start(struct ib_block_iter *biter, {
> > __rdma_block_iter_start(biter, umem->sgt_append.sgt.sgl,
> > umem->sgt_append.sgt.nents, pgsz);
> > + biter->__sg_advance = ib_umem_offset(umem) & ~(pgsz - 1);
> > + biter->__sg_numblocks = ib_umem_num_dma_blocks(umem, pgsz);
> > }
> >
> > /**
> > @@ -92,7 +94,7 @@ static inline void __rdma_umem_block_iter_start(struct
> ib_block_iter *biter,
> > */
> > #define rdma_umem_for_each_dma_block(umem, biter, pgsz) \
> > for (__rdma_umem_block_iter_start(biter, umem, pgsz); \
> > - __rdma_block_iter_next(biter);)
> > + __rdma_block_iter_next(biter) && (biter)->__sg_numblocks--;)
>
> This sg_numblocks should be in the __rdma_block_iter_next() ?
>
> It makes sense to me
>
The __rdma_block_iter_next() is common to two iterators: rdma_umem_for_each_dma_block() and rdma_for_each_block.
The patch makes adjustments to protect users of rdma_for_each_block().
We are working on a v2 to add a umem specific next function that will implement the downcount.
