linux-kernel - Re: DMA error when sg->offset value is greater than PAGE

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Message-ID: <MWHPR12MB160060436AC70CB5BE8C0C6EC8780@MWHPR12MB1600.namprd12.prod.outlook.com>
Date:   Wed, 27 Sep 2017 16:31:04 +0000
From:   Casey Leedom <leedom@...lsio.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Robin Murphy <robin.murphy@....com>,
        "Harsh Jain" <Harsh@...lsio.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Woodhouse <David.Woodhouse@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        Michael Werner <werner@...lsio.com>
Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in
 Intel IOMMU

| From: Dan Williams <dan.j.williams@...el.com>
| Sent: Tuesday, September 26, 2017 9:10 AM
|   
| On Tue, Sep 26, 2017 at 9:06 AM, Casey Leedom <leedom@...lsio.com> wrote:
| > | From: Robin Murphy <robin.murphy@....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 ...

Casey