Re: [PATCH v2 for-rc 1/3] RDMA/core: Fix umem iterator when PAGE_SIZE is greater then HCA pgsz

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Nov 29, 2023 at 02:21:41PM -0600, Shiraz Saleem wrote:
> be arbitrary, but for 64k pages, the VA may be offset by some
> number of HCA 4k pages and followed by some number of HCA 4k
> pages.
> 
> The current iterator doesn't account for either the preceding
> 4k pages or the following 4k pages.
> 
> Fix the issue by extending the ib_block_iter to contain
> the number of DMA pages like comment [1] says and by using
> __sg_advance to start the iterator at the first live HCA page.
> 
> The changes are contained in a parallel set of iterator start
> and next functions that are umem aware and specfic to umem
> since there is one user of the rdma_for_each_block() without
> umem.
> 
> These two fixes prevents the extra pages before and after the
> user MR data.
> 
> Fix the preceding pages by using the __sq_advance field to start
> at the first 4k page containing MR data.
> 
> Fix the following pages by saving the number of pgsz blocks in
> the iterator state and downcounting on each next.
> 
> This fix allows for the elimination of the small page crutch noted
> in the Fixes.
> 
> Fixes: 10c75ccb54e4 ("RDMA/umem: Prevent small pages from being returned by ib_umem_find_best_pgsz()")
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/rdma/ib_umem.h#n91 [1]
> Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
> Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
> ---
>  drivers/infiniband/core/umem.c | 6 ------
>  include/rdma/ib_umem.h         | 9 ++++++++-
>  include/rdma/ib_verbs.h        | 1 +
>  3 files changed, 9 insertions(+), 7 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

I admit this fix looks so easy and simple I wonder if there was some
tricky reason why I didn't do it back then.. Oh well, I've forgotten,
I guess we will find out!

Jason