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

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Message-ID: <CAPcyv4ihhJM5+iHTMzH2m5n7X5347MHkj0h2DC5KGobjby5nmg@mail.gmail.com>
Date:   Mon, 25 Sep 2017 13:11:04 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Casey Leedom <leedom@...lsio.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Harsh Jain <Harsh@...lsio.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>,
        David Woodhouse <David.Woodhouse@...el.com>
Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in
 Intel IOMMU

On Mon, Sep 25, 2017 at 1:05 PM, Casey Leedom <leedom@...lsio.com> wrote:
> | From: Dan Williams <dan.j.williams@...el.com>
> | 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.