linux-kernel - Re: [PATCH v3 02/20] PCI/P2PDMA: attempt to set map

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Date:   Mon, 27 Sep 2021 13:50:36 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     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,
        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>,
        John Hubbard <jhubbard@...dia.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>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>
Subject: Re: [PATCH v3 02/20] PCI/P2PDMA: attempt to set map_type if it has
 not been set

On Thu, Sep 16, 2021 at 05:40:42PM -0600, Logan Gunthorpe wrote:
> Attempt to find the mapping type for P2PDMA pages on the first
> DMA map attempt if it has not been done ahead of time.
> 
> Previously, the mapping type was expected to be calculated ahead of
> time, but if pages are to come from userspace then there's no
> way to ensure the path was checked ahead of time.
> 
> With this change it's no longer invalid to call pci_p2pdma_map_sg()
> before the mapping type is calculated so drop the WARN_ON when that
> is the case.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

Capitalize subject line.

> ---
>  drivers/pci/p2pdma.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 50cdde3e9a8b..1192c465ba6d 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -848,6 +848,7 @@ static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
>  	struct pci_dev *provider = to_p2p_pgmap(pgmap)->provider;
>  	struct pci_dev *client;
>  	struct pci_p2pdma *p2pdma;
> +	int dist;
>  
>  	if (!provider->p2pdma)
>  		return PCI_P2PDMA_MAP_NOT_SUPPORTED;
> @@ -864,6 +865,10 @@ static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
>  		type = xa_to_value(xa_load(&p2pdma->map_types,
>  					   map_types_idx(client)));
>  	rcu_read_unlock();
> +
> +	if (type == PCI_P2PDMA_MAP_UNKNOWN)
> +		return calc_map_type_and_dist(provider, client, &dist, false);
> +
>  	return type;
>  }
>  
> @@ -906,7 +911,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
>  	case PCI_P2PDMA_MAP_BUS_ADDR:
>  		return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents);
>  	default:
> -		WARN_ON_ONCE(1);
>  		return 0;
>  	}
>  }
> -- 
> 2.30.2
>