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

Sebastian Ott
2025-12-10T17:12:08Z

On Wed, 10 Dec 2025, Chaitanya Kulkarni wrote:
> (+ Leon Romanovsky)
>
> On 12/9/25 20:05, Keith Busch wrote:
>> 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.
>
> Thanks for catching that, see updated version of this patch [1].
>
>> 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.
>
> That's why I've asked reporter to test it.
>
> Either way, IMO both of the patches are still needed.
>

The patch Keith posted fixes the issue for me. Should I do another run
with only these 2 applied?