nvme-pci: limit max_hw_sectors based on the DMA max mapping size

When running a NVMe device that is attached to a addressing
challenged PCIe root port that requires bounce buffering, our
request sizes can easily overflow the swiotlb bounce buffer
size.  Limit the maximum I/O size to the limit exposed by
the DMA mapping subsystem.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reported-by: NAtish Patra <Atish.Patra@wdc.com>
Tested-by: NAtish Patra <Atish.Patra@wdc.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>

drivers/nvme/host/pci.c

@@ -2503,7 +2503,8 @@ static void nvme_reset_work(struct work_struct *work)
 	 * Limit the max command size to prevent iod->sg allocations going
 	 * over a single page.
 	 */
-	dev->ctrl.max_hw_sectors = NVME_MAX_KB_SZ << 1;
+	dev->ctrl.max_hw_sectors = min_t(u32,
+		NVME_MAX_KB_SZ << 1, dma_max_mapping_size(dev->dev) >> 9);
 	dev->ctrl.max_segments = NVME_MAX_SEGS;
 
 	/*