From: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in
	Intel IOMMU
Date: Mon, 25 Sep 2017 13:11:04 -0700
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To: Casey Leedom <leedom-ut6Up61K2wZBDgjK7y7TUQ@public.gmane.org>
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On Mon, Sep 25, 2017 at 1:05 PM, Casey Leedom <leedom-ut6Up61K2wZBDgjK7y7TUQ@public.gmane.org> wrote:
> | From: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> | Sent: Monday, September 25, 2017 12:31 PM
> | ...
> | IIUC it looks like this has been broken ever since commit e1605495c716
> | "intel-iommu: Introduce domain_sg_mapping() to speed up
> | intel_map_sg()". I.e. it looks like the calculation for pte_val should
> | be:
> |
> |     pteval = (page_to_phys(sg_page(sg)) + sg->offset) | prot;
>
> Hhmmm, shouldn't that be:
>
>     pteval = (page_to_phys(sg_page(sg)) + (sg->offset>>PAGE_SHIFT)) | prot;

Yes, I think you're right. We do want to mask off the page-unaligned
portion of sg->offset.