linux-kernel - Re: [PATCH v10 23/24] nvme-pci: convert to blk_rq_dma

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Message-ID: <aA-w20gOKus5hyAV@kbusch-mbp.dhcp.thefacebook.com>
Date: Mon, 28 Apr 2025 10:46:19 -0600
From: Keith Busch <kbusch@...nel.org>
To: Leon Romanovsky <leon@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Jake Edge <jake@....net>, Jonathan Corbet <corbet@....net>,
	Jason Gunthorpe <jgg@...pe.ca>, Zhu Yanjun <zyjzyj2000@...il.com>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	linux-pci@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Kanchan Joshi <joshi.k@...sung.com>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Nitesh Shetty <nj.shetty@...sung.com>,
	Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH v10 23/24] nvme-pci: convert to blk_rq_dma_map

On Mon, Apr 28, 2025 at 12:22:29PM +0300, Leon Romanovsky wrote:
> +	do {
> +		if (WARN_ON_ONCE(mapped == entries)) {
> +			iter.status = BLK_STS_IOERR;
> +			break;
> +		}
> +		nvme_pci_sgl_set_data(&sg_list[mapped++], &iter);

I think this should say "++mapped" so that the data blocks start at
index 1 (continued below...)

> +		iod->total_len += iter.len;
> +	} while (blk_rq_dma_map_iter_next(req, dev->dev, &iod->dma_meta_state,
> +				 &iter));
>  
> -out_unmap_sg:
> -	dma_unmap_sgtable(dev->dev, &iod->meta_sgt, rq_dma_dir(req), 0);
> -out_free_sg:
> -	mempool_free(iod->meta_sgt.sgl, dev->iod_meta_mempool);
> -	return BLK_STS_RESOURCE;
> +	nvme_pci_sgl_set_seg(sg_list, sgl_dma, mapped);

because this here is setting sg_list index 0 to be the segment
descriptor.

And you also need to increment sgl_dma to point to the element after
sg_list, otherwise it's pointing right back to itself, creating a looped
list.

> +	if (unlikely(iter.status))
> +		nvme_unmap_metadata(dev, req);
> +	return iter.status;
>  }