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

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Message-ID: <aGMxu6Yn514Xy55w@kbusch-mbp>
Date: Mon, 30 Jun 2025 18:54:19 -0600
From: Keith Busch <kbusch@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Ben Copeland <ben.copeland@...aro.org>, linux-kernel@...r.kernel.org,
	lkft-triage@...ts.linaro.org, regressions@...ts.linux.dev,
	linux-nvme@...ts.infradead.org,
	Dan Carpenter <dan.carpenter@...aro.org>, axboe@...nel.dk,
	sagi@...mberg.me, iommu@...ts.linux.dev
Subject: Re: next-20250627: IOMMU DMA warning during NVMe I/O completion
 after 06cae0e3f61c

On Mon, Jun 30, 2025 at 02:25:23PM -0600, Keith Busch wrote:
> On Mon, Jun 30, 2025 at 03:33:43PM +0200, Christoph Hellwig wrote:
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -701,7 +701,7 @@ static void nvme_free_prps(struct request *req)
>         prp_list = iod->descriptors[desc];
>         do {
>                 dma_unmap_page(dma_dev, dma_addr, dma_len, dir);
> -               if (i == NVME_CTRL_PAGE_SIZE >> 3) {
> +               if (i == NVME_CTRL_PAGE_SIZE >> 3 && length > NVME_CTRL_PAGE_SIZE) {
>                         prp_list = iod->descriptors[++desc];
>                         i = 0;
>                 }
> --
> 
> But even that, the PRP setup doesn't match the teardown. We're calling
> dma_map_page() on each PRP even if consecutive PRP's [...]

Err, I meant to say "dma_unmap_page()".