> On Feb 12, 2020, at 2:30 PM, Jason Gunthorpe <jgg@xxxxxxxx> wrote:
>
> On Wed, Feb 12, 2020 at 02:09:03PM -0500, Chuck Lever wrote:
>>
>>
>>> 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?
>
> I imagine it would get you on ARM or other archs, IIRC.
That's certainly plausible, but I haven't received explicit bug reports
in this area. (I'm not at all saying that such bugs categorically do
not exist).
In any event, practical matters: the posted patch applies back to v5.4,
but fails to apply starting with v5.3.
I think we can leave the "Cc: stable # v5.5"; and I'm open to requests
to backport this simple fix onto earlier stable kernels (back to v4.4),
which can be handled case-by-case. 'Salright?
--
Chuck Lever
