On Thu, Feb 13, 2020 at 09:33:23AM -0500, Chuck Lever wrote:
>
>
> > 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).
Usually I encourage people to put the fixes line to the commit that is
being fixed, pointing at some other commit that happens to expose the
bug is not the best.
> 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?
I'd just put Cc: stable, the stable folks will reject it on earlier
versions because of conflicts and we can leave it.
Jason
