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

[Keith Busch <kbusch@kernel.org>]

On Wed, Dec 10, 2025 at 02:02:43PM +0900, Keith Busch wrote:
> On Tue, Dec 09, 2025 at 12:43:31PM +0100, Sebastian Ott wrote:
> > got the following warning after a kernel update on Thurstday, leading to a
> > panic and fs corruption. I didn't capture the first warning but I'm pretty
> > sure it was the same. It's reproducible but I didn't bisect since it
> > borked my fs. The only hint I can give is that v6.18 worked. Is this a
> > known issue? Anything I should try?
> 
> Could you check if your nvme device supports SGLs? There are some new
> features in 6.19 that would allow merging IO that wouldn't have happened
> before. You can check from command line:

Actually the SGL support is probably unnecessary for ARM if your iommu
granularity is 64k. That setup could also lead to an uninitialized
"state" and the type of corruption you're observing. But the same patch
below is still the proposed fix for it anyway.
 
> ---
> diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
> index e9108ccaf4b06..7bff480d666e2 100644
> --- a/block/blk-mq-dma.c
> +++ b/block/blk-mq-dma.c
> @@ -199,6 +199,7 @@ static bool blk_dma_map_iter_start(struct request *req, struct device *dma_dev,
>  	if (blk_can_dma_map_iova(req, dma_dev) &&
>  	    dma_iova_try_alloc(dma_dev, state, vec.paddr, total_len))
>  		return blk_rq_dma_map_iova(req, dma_dev, state, iter, &vec);
> +	state->__size = 0;
>  	return blk_dma_map_direct(req, dma_dev, iter, &vec);
>  }
> 
> --
>