linux-kernel - Re: [PATCH 6/6] scatterlist: use sg

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Date:	Fri, 7 Aug 2015 18:15:49 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-crypto@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH 6/6] scatterlist: use sg_phys()

On Fri, Aug 7, 2015 at 9:15 AM, Christoph Hellwig <hch@....de> wrote:
> From: Dan Williams <dan.j.williams@...el.com>
>
> Coccinelle cleanup to replace open coded sg to physical address
> translations.  This is in preparation for introducing scatterlists that
> reference __pfn_t.
>
> // sg_phys.cocci: convert usage page_to_phys(sg_page(sg)) to sg_phys(sg)
> // usage: make coccicheck COCCI=sg_phys.cocci MODE=patch
>
> virtual patch
> virtual report
> virtual org
>
> @@
> struct scatterlist *sg;
> @@
>
> - page_to_phys(sg_page(sg)) + sg->offset
> + sg_phys(sg)
>
> @@
> struct scatterlist *sg;
> @@
>
> - page_to_phys(sg_page(sg))
> + sg_phys(sg) - sg->offset

So this ends up being an awkward conversion, a better one is:

- page_to_phys(sg_page(sg))
+ sg_phys(sg) & PAGE_MASK

[..]
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 5852df8..e0faecc 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2098,7 +2098,7 @@ static int __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
>                         sg_res = aligned_nrpages(sg->offset, sg->length);
>                         sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + sg->offset;
>                         sg->dma_length = sg->length;
> -                       pteval = page_to_phys(sg_page(sg)) | prot;
> +                       pteval = (sg_phys(sg) - sg->offset) | prot;

For example here, as Joerg pointed out.

[1]: https://lkml.org/lkml/2015/6/10/230
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