Re: [PATCH v3 1/2] xprtrdma: Fix DMA scatter-gather list mapping imbalance

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Feb 12, 2020 at 11:12:30AM -0500, Chuck Lever wrote:
> The @nents value that was passed to ib_dma_map_sg() has to be passed
> to the matching ib_dma_unmap_sg() call. If ib_dma_map_sg() choses to
> concatenate sg entries, it will return a different nents value than
> it was passed.
> 
> The bug was exposed by recent changes to the AMD IOMMU driver, which
> enabled sg entry concatenation.
> 
> Looking all the way back to commit 4143f34e01e9 ("xprtrdma: Port to
> new memory registration API") and reviewing other kernel ULPs, it's
> not clear that the frwr_map() logic was ever correct for this case.
> 
> Reported-by: Andre Tomt <andre@tomt.net>
> Suggested-by: Robin Murphy <robin.murphy@arm.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> Cc: stable@vger.kernel.org # v5.5
> ---
>  net/sunrpc/xprtrdma/frwr_ops.c |   13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)

Yep

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

Jason