> On Feb 12, 2020, at 2:05 PM, Jason Gunthorpe <jgg@xxxxxxxx> wrote:
>
> On Wed, Feb 12, 2020 at 01:38:59PM -0500, Chuck Lever wrote:
>>
>>> On Feb 12, 2020, at 1:26 PM, Jason Gunthorpe <jgg@xxxxxxxx> wrote:
>>>
>>> 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@xxxxxxxx>
>>>> Suggested-by: Robin Murphy <robin.murphy@xxxxxxx>
>>>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>>> Cc: stable@xxxxxxxxxxxxxxx # v5.5
>>>> net/sunrpc/xprtrdma/frwr_ops.c | 13 +++++++------
>>>> 1 file changed, 7 insertions(+), 6 deletions(-)
>>>
>>> Yep
>>>
>>> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
>>
>> Thanks.
>>
>> Wondering if it makes sense to add a Fixes tag for the AMD IOMMU commit
>> where NFS/RDMA stopped working, rather than the "Cc: stable # v5.5".
>>
>> Fixes: be62dbf554c5 ("iommu/amd: Convert AMD iommu driver to the dma-iommu api")
>
> Not really, this was broken for other configurations besides AMD
Agreed, but the bug seems to have been inconsequential until now?
Otherwise we should explore backporting farther into the past.
--
Chuck Lever
