linux-kernel - Re: [PATCH 07/16] PCI/P2PDMA: Make pci_p2pdma_map

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Message-ID: <31b17b7d-f6de-c205-d1a3-e570928605f4@deltatee.com>
Date:   Mon, 3 May 2021 10:39:53 -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 07/16] PCI/P2PDMA: Make pci_p2pdma_map_type() non-static



On 2021-05-02 4:44 p.m., John Hubbard wrote:
> On 4/8/21 10:01 AM, Logan Gunthorpe wrote:
>> pci_p2pdma_map_type() will be needed by the dma-iommu map_sg
>> implementation because it will need to determine the mapping type
>> ahead of actually doing the mapping to create the actual iommu mapping.
>>
>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>> ---
>>   drivers/pci/p2pdma.c       | 34 +++++++++++++++++++++++-----------
>>   include/linux/pci-p2pdma.h | 15 +++++++++++++++
>>   2 files changed, 38 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>> index bcb1a6d6119d..38c93f57a941 100644
>> --- a/drivers/pci/p2pdma.c
>> +++ b/drivers/pci/p2pdma.c
>> @@ -20,13 +20,6 @@
>>   #include <linux/seq_buf.h>
>>   #include <linux/xarray.h>
>>   
>> -enum pci_p2pdma_map_type {
>> -	PCI_P2PDMA_MAP_UNKNOWN = 0,
>> -	PCI_P2PDMA_MAP_NOT_SUPPORTED,
>> -	PCI_P2PDMA_MAP_BUS_ADDR,
>> -	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
>> -};
>> -
>>   struct pci_p2pdma {
>>   	struct gen_pool *pool;
>>   	bool p2pmem_published;
>> @@ -822,13 +815,30 @@ void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
>>   }
>>   EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
>>   
>> -static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
>> -						    struct device *dev)
>> +/**
>> + * pci_p2pdma_map_type - return the type of mapping that should be used for
>> + *	a given device and pgmap
>> + * @pgmap: the pagemap of a page to determine the mapping type for
>> + * @dev: device that is mapping the page
>> + * @dma_attrs: the attributes passed to the dma_map operation --
>> + *	this is so they can be checked to ensure P2PDMA pages were not
>> + *	introduced into an incorrect interface (like dma_map_sg). *
>> + *
>> + * Returns one of:
>> + *	PCI_P2PDMA_MAP_NOT_SUPPORTED - The mapping should not be done
>> + *	PCI_P2PDMA_MAP_BUS_ADDR - The mapping should use the PCI bus address
>> + *	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE - The mapping should be done directly
>> + */
>> +enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
>> +		struct device *dev, unsigned long dma_attrs)
>>   {
>>   	struct pci_dev *provider = to_p2p_pgmap(pgmap)->provider;
>>   	enum pci_p2pdma_map_type ret;
>>   	struct pci_dev *client;
>>   
>> +	WARN_ONCE(!(dma_attrs & __DMA_ATTR_PCI_P2PDMA),
>> +		  "PCI P2PDMA pages were mapped with dma_map_sg!");
> 
> This really ought to also return -EINVAL, assuming that my review suggestions
> about return types, in earlier patches, are acceptable.

That can't happen because, by convention, dma_map_sg() cannot return
-EINVAL. I think the best we can do is proceed normally and just warn
loudly.

Logan