linux-kernel - Re: [PATCH 13/16] nvme-pci: Convert to using dma_map_sg

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Date:   Sun, 2 May 2021 18:34:39 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>
CC:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 13/16] nvme-pci: Convert to using dma_map_sg_p2pdma for
 p2pdma pages

On 4/8/21 10:01 AM, Logan Gunthorpe wrote:
> Convert to using dma_map_sg_p2pdma() for PCI p2pdma pages.
> 
> This should be equivalent but allows for heterogeneous scatterlists
> with both P2PDMA and regular pages. However, P2PDMA support will be
> slightly more restricted (only dma-direct and dma-iommu are currently
> supported).
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>   drivers/nvme/host/pci.c | 28 ++++++++--------------------
>   1 file changed, 8 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 14f092973792..a1ed07ff38b7 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -577,17 +577,6 @@ static void nvme_free_sgls(struct nvme_dev *dev, struct request *req)
>   
>   }
>   
> -static void nvme_unmap_sg(struct nvme_dev *dev, struct request *req)
> -{
> -	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> -
> -	if (is_pci_p2pdma_page(sg_page(iod->sg)))
> -		pci_p2pdma_unmap_sg(dev->dev, iod->sg, iod->nents,
> -				    rq_dma_dir(req));
> -	else
> -		dma_unmap_sg(dev->dev, iod->sg, iod->nents, rq_dma_dir(req));
> -}
> -
>   static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
>   {
>   	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> @@ -600,7 +589,7 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
>   
>   	WARN_ON_ONCE(!iod->nents);
>   
> -	nvme_unmap_sg(dev, req);
> +	dma_unmap_sg(dev->dev, iod->sg, iod->nents, rq_dma_dir(req));


Nice simplification!


>   	if (iod->npages == 0)
>   		dma_pool_free(dev->prp_small_pool, nvme_pci_iod_list(req)[0],
>   			      iod->first_dma);
> @@ -868,14 +857,13 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>   	if (!iod->nents)
>   		goto out_free_sg;
>   
> -	if (is_pci_p2pdma_page(sg_page(iod->sg)))
> -		nr_mapped = pci_p2pdma_map_sg_attrs(dev->dev, iod->sg,
> -				iod->nents, rq_dma_dir(req), DMA_ATTR_NO_WARN);
> -	else
> -		nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents,
> -					     rq_dma_dir(req), DMA_ATTR_NO_WARN);
> -	if (!nr_mapped)
> +	nr_mapped = dma_map_sg_p2pdma_attrs(dev->dev, iod->sg, iod->nents,
> +				     rq_dma_dir(req), DMA_ATTR_NO_WARN);
> +	if (nr_mapped < 0) {
> +		if (nr_mapped != -ENOMEM)
> +			ret = BLK_STS_TARGET;
>   		goto out_free_sg;
> +	}

But now the "nr_mapped == 0" case is no longer doing an early out_free_sg.
Is that OK?

>   
>   	iod->use_sgl = nvme_pci_use_sgls(dev, req);
>   	if (iod->use_sgl)
> @@ -887,7 +875,7 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>   	return BLK_STS_OK;
>   
>   out_unmap_sg:
> -	nvme_unmap_sg(dev, req);
> +	dma_unmap_sg(dev->dev, iod->sg, iod->nents, rq_dma_dir(req));
>   out_free_sg:
>   	mempool_free(iod->sg, dev->iod_mempool);
>   	return ret;
> 

thanks,
-- 
John Hubbard
NVIDIA