linux-kernel - Re: [PATCH] iommu/vt-d: Fix scatterlist offset handling

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Message-ID: <20170928154345.GA101272@otc-nc-03>
Date:   Thu, 28 Sep 2017 08:43:46 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Casey Leedom <leedom@...lsio.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        Harsh Jain <Harsh@...lsio.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Werner <werner@...lsio.com>,
        Atul Gupta <atul.gupta@...lsio.com>
Subject: Re: [PATCH] iommu/vt-d: Fix scatterlist offset handling

Hi Robin

thanks.. i have no idea.. i see all the other patches from you :-)
my email has decided to play games with me i suppose :-)

On Thu, Sep 28, 2017 at 05:59:11PM +0100, Robin Murphy wrote:
> I hope our email server hasn't got blacklisted again... Said patch is
> the top of this very thread we're replying on[1] - you were definitely
> on cc :(

        (sg->dma_address + sg->dma_len) ----+
        sg->dma_address ---------+          |
        iov_pfn------+           |          |
                     |           |          |
                     v           v          v
    iova:   a        b        c        d        e        f
            |--------|--------|--------|--------|--------|
                              <...calculated....>
                     [_____mapped______]
    pfn:    0        1        2        3        4        5
            |--------|--------|--------|--------|--------|
                     ^           ^          ^
                     |           |          |
        sg->page ----+           |          |
        sg->offset --------------+          |
        (sg->offset + sg->length) ----------+

The picture seems right. Looking at the code i'm not sure if i understand
it correctly.

pgoff = sg->offset & ~PAGE_MASK;

this gets the offset past the start of page.

sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + pgoff;

this would set dma_address at b+off instead of starting at c+off correct?

> 
> Robin
> 
> [1]:https://lists.linuxfoundation.org/pipermail/iommu/2017-September/024371.html