Re: WARNING: drivers/iommu/io-pgtable-arm.c:639

Keith Busch
2025-12-10T04:05:45Z

On Wed, Dec 10, 2025 at 02:30:50AM +0000, Chaitanya Kulkarni wrote:
> @@ -126,17 +126,26 @@ static bool blk_rq_dma_map_iova(struct request *req, struct device *dma_dev,
> error = dma_iova_link(dma_dev, state, vec->paddr, mapped,
> vec->len, dir, attrs);
> if (error)
> - break;
> + goto out_unlink;
> mapped += vec->len;
> } while (blk_map_iter_next(req, &iter->iter, vec));
>
> error = dma_iova_sync(dma_dev, state, 0, mapped);
> - if (error) {
> - iter->status = errno_to_blk_status(error);
> - return false;
> - }
> + if (error)
> + goto out_unlink;
>
> return true;
> +
> +out_unlink:
> + /*
> + * Unlink any partial mapping to avoid unmap mismatch later.
> + * If we mapped some bytes but not all, we must clean up now
> + * to prevent attempting to unmap more than was actually mapped.
> + */
> + if (mapped)
> + dma_iova_unlink(dma_dev, state, 0, mapped, dir, attrs);
> + iter->status = errno_to_blk_status(error);
> + return false;
> }

It does look like a bug to continue on when dma_iova_link() fails as the
caller thinks the entire mapping was successful, but I think you also
need to call dma_iova_free() to undo the earlier dma_iova_try_alloc(),
otherwise iova space is leaked.

I'm a bit doubtful this error condition was hit though: this sequence
is largely the same as it was in v6.18 before the regression. The only
difference since then should just be for handling P2P DMA across a host
bridge, which I don't think applies to the reported bug since that's a
pretty unusual thing to do.