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SubjectRe: DMA error when sg->offset value is greater than PAGE_SIZE in Intel IOMMU
On Wed, Sep 27, 2017 at 9:31 AM, Casey Leedom <leedom@chelsio.com> wrote:
> | From: Dan Williams <dan.j.williams@intel.com>
> | Sent: Tuesday, September 26, 2017 9:10 AM
> |
> | On Tue, Sep 26, 2017 at 9:06 AM, Casey Leedom <leedom@chelsio.com> wrote:
> | > | From: Robin Murphy <robin.murphy@arm.com>
> | > | Sent: Tuesday, September 26, 2017 7:22 AM
> | > |...
> | > ...
> | > Regardless, it seems that you agree that there's an issue with the Intel
> | > I/O MMU support code with regard to the legal values which a (struct
> | > scatterlist) can take on? I still can't find any documentation for this
> | > and, personally, I'm a bit baffled by a Page-oriented Scatter/Gather List
> | > representation where [Offset, Offset+Length) can reside outside the Page.
> |
> | Consider the case where the page represents a huge page, then an
> | offset greater than PAGE_SIZE (up to HPAGE_SIZE) makes sense.
>
> Okay, but whatever the underlaying Page Size is, should [Offset,
> Offset+Length) completely reside within the referenced Page? I'm just
> trying to understand the Invariance Conditions which are assumed by all of
> the code which processes Scatter/gather Lists ...

As far as I can see "Offset can be greater than PAGE_SIZE" is the only
safe assumption for core code.

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