Re: [PATCH v2] xprtrdma: Fix DMA scatter-gather list mapping imbalance

[Chuck Lever <chuck.lever@oracle.com>]

> On Feb 12, 2020, at 11:03 AM, Andre Tomt <andre@tomt.net> wrote:
> 
> On 12.02.2020 14:48, Chuck Lever wrote:
>>> On Feb 12, 2020, at 8:43 AM, Chuck Lever <chuck.lever@oracle.com> 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 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>
>>> ---
>>> include/trace/events/rpcrdma.h |    6 ++++--
>>> net/sunrpc/xprtrdma/frwr_ops.c |   13 +++++++------
>>> 2 files changed, 11 insertions(+), 8 deletions(-)
>>> 
>>> Hi Andre, here's take 2, based on the trace data you sent me.
>>> Please let me know if this one fares any better.
>>> 
>>> Changes since v1:
>>> - Ensure the correct nents value is passed to ib_map_mr_sg
>>> - Record the mr_nents value in the MR trace points
> Verified working (with the patch correction) in my environment, with some quick testing (mount + some random and bulk I/O)
> 
> client, 5.5.3 + patch + amd iommu on = OK
> client, 5.5.3 + patch + amd iommu off = OK
> client, 5.6-rc1 + patch + amd iommu on = OK
> 
> server, 5.5.3 + patch + intel iommu on = OK

Very good! I'll submit the fix through the NFS tree ASAP, and request backport to v5.5 stable.

--
Chuck Lever