Re: next-20250627: IOMMU DMA warning during NVMe I/O completion after 06cae0e3f61c

[Kanchan Joshi <joshi.k@samsung.com>]

On 6/30/2025 1:20 PM, Ben Copeland wrote:
> # first bad commit: [06cae0e3f61c4c1ef18726b817bbb88c29f81e57]
> nvme-pci: merge the simple PRP and SGL setup into a common helper

this patch had the problem [0] of not setting 'iod->first_dma' which can 
trigger that IOMMU warning on unmap.
But problem was transient as a subsequent patch removed the 
iod->first_dma and made unmapping work without that.

[0]
-static blk_status_t nvme_setup_prp_simple(struct nvme_dev *dev,
-               struct request *req, struct nvme_rw_command *cmnd,
-               struct bio_vec *bv)
+static blk_status_t nvme_pci_setup_data_simple(struct request *req,
+               enum nvme_use_sgl use_sgl)
  {
         struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
-       unsigned int offset = bv->bv_offset & (NVME_CTRL_PAGE_SIZE - 1);
-       unsigned int first_prp_len = NVME_CTRL_PAGE_SIZE - offset;
-
-       iod->first_dma = dma_map_bvec(dev->dev, bv, rq_dma_dir(req), 0);
-       if (dma_mapping_error(dev->dev, iod->first_dma))

iod->first_dma does not get set, and that can cause unmap on invalid 
address during teardown.