linux-kernel - Re: [PATCH 14/16] nvme-rdma: Ensure dma support when using p2pdma

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Date:   Sun, 2 May 2021 18:37:22 -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 14/16] nvme-rdma: Ensure dma support when using p2pdma

On 4/8/21 10:01 AM, Logan Gunthorpe wrote:
> Ensure the dma operations support p2pdma before using the RDMA
> device for P2PDMA. This allows switching the RDMA driver from
> pci_p2pdma_map_sg() to dma_map_sg_p2pdma().

Tentatively, this looks right, but it really should be combined
with a following patch that uses it. Then you don't have to try
to explain, above, why it's needed. :)

> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>   drivers/nvme/target/rdma.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/target/rdma.c b/drivers/nvme/target/rdma.c
> index 6c1f3ab7649c..3ec7e77e5416 100644
> --- a/drivers/nvme/target/rdma.c
> +++ b/drivers/nvme/target/rdma.c
> @@ -414,7 +414,8 @@ static int nvmet_rdma_alloc_rsp(struct nvmet_rdma_device *ndev,
>   	if (ib_dma_mapping_error(ndev->device, r->send_sge.addr))
>   		goto out_free_rsp;
>   
> -	if (!ib_uses_virt_dma(ndev->device))
> +	if (!ib_uses_virt_dma(ndev->device) &&
> +	    dma_pci_p2pdma_supported(&ndev->device->dev))
>   		r->req.p2p_client = &ndev->device->dev;
>   	r->send_sge.length = sizeof(*r->req.cqe);
>   	r->send_sge.lkey = ndev->pd->local_dma_lkey;
> 

thanks,
-- 
John Hubbard
NVIDIA