On Thu, Sep 03, 2020 at 02:11:37PM +0000, Saleem, Shiraz wrote:
> > Subject: [PATCH 02/14] RDMA/umem: Prevent small pages from being returned by
> > ib_umem_find_best_pgsz()
> >
> > rdma_for_each_block() makes assumptions about how the SGL is constructed that
> > don't work if the block size is below the page size used to to build the SGL.
> >
> > The rules for umem SGL construction require that the SG's all be PAGE_SIZE
> > aligned and we don't encode the actual byte offset of the VA range inside the SGL
> > using offset and length. So rdma_for_each_block() has no idea where the actual
> > starting/ending point is to compute the first/last block boundary if the starting
> > address should be within a SGL.
>
> Not sure if we were exposed today. i.e. rdma drivers working with
> block sizes smaller than system page size?
Yes, it could happen, here are some examples:
drivers/infiniband/hw/i40iw/i40iw_verbs.c:
iwmr->page_size = ib_umem_find_best_pgsz(region, SZ_4K | SZ_2M,
drivers/infiniband/hw/bnxt_re/ib_verbs.c:
page_shift = __ffs(ib_umem_find_best_pgsz(umem,
BNXT_RE_PAGE_SIZE_4K | BNXT_RE_PAGE_SIZE_2M,
virt_addr));
Eg that breaks on a ARM with 16k or 64k page sizes.
Jason
