On 11/02/2020 4:03 pm, Chuck Lever wrote:
On Feb 11, 2020, at 10:32 AM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
On 11/02/2020 3:24 pm, Chuck Lever wrote:
On Feb 11, 2020, at 10:12 AM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
On 11/02/2020 1:48 pm, Chuck Lever wrote:
Andre-
Thank you for the detailed report!
Tom-
There is a rich set of trace points available in the RPC/RDMA implementation in 5.4/5.5, fwiw.
Please keep me in the loop, let me know if there is anything I can do to help.
One aspect that may be worth checking is whether there's anywhere that assumes a successful return value from dma_map_sg() is always the same as the number of entries passed in - that's the most obvious way the iommu-dma code differs (legitimately) from the previous amd-iommu implementation.
net/sunrpc/xprtrdma/frwr_ops.c: frwr_map()
317 mr->mr_nents =
318 ib_dma_map_sg(ia->ri_id->device, mr->mr_sg, i, mr->mr_dir);
319 if (!mr->mr_nents)
320 goto out_dmamap_err;
Should that rather be "if (mr->mr_nents != i)" ?
No, that much is OK - the point is that dma_map_sg() may pack the DMA addresses such that sg_dma_len(sg) > sg->length - however, subsequently passing that mr->nents to dma_unmap_sg() in frwr_mr_recycle() (rather than the original value of i) looks at a glance like an example of how things may start to get out-of-whack.
Robin, your explanation makes sense to me. I can post a fix for this imbalance later today for Andre to try.
FWIW here's a quick hack which *should* suppress the concatenation
behaviour - if it makes Andre's system any happier then that would
indeed point towards dma_map_sg() handling being the culprit.
Robin.
----->8-----
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index a2e96a5fd9a7..a6b71bad518e 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -779,7 +779,7 @@ static int __finalise_sg(struct device *dev, struct
scatterlist *sg, int nents,
* - but doesn't fall at a segment boundary
* - and wouldn't make the resulting output segment too long
*/
- if (cur_len && !s_iova_off && (dma_addr & seg_mask) &&
+ if (0 && cur_len && !s_iova_off && (dma_addr & seg_mask) &&
(max_len - cur_len >= s_length)) {
/* ...then concatenate it with the previous one */
cur_len += s_length;
@@ -799,6 +799,7 @@ static int __finalise_sg(struct device *dev, struct
scatterlist *sg, int nents,
if (s_length + s_iova_off < s_iova_len)
cur_len = 0;
}
+ WARN_ON(count < nents);
return count;
}
