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

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Date:   Mon, 3 May 2021 11:19:32 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     John Hubbard <jhubbard@...dia.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 2021-05-02 7:34 p.m., John Hubbard wrote:
>>   	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?

dma_map_sg_p2pdma_attrs() never returns zero. It will return -ENOMEM in
the same situation and results in the same goto out_free_sg.

Logan