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SubjectRe: [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

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