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SubjectRe: DMA error when sg->offset value is greater than PAGE_SIZE in Intel IOMMU
Hi Casey

looking at the debug output i got from Harsh it still looks like
a bug in the code.

[ 538.284589] __domain_mapping nr_pages 0x1
[ 538.284600] __domain_mapping sg_res 0x1 sg->dma_address 0xf291000e dma len 0x38 pteval 0x3cbce3003 phys_pfn 0x3cbce3
[ 538.284604] chelsio driver - offset 4110 len 56 dma addr f291000e dma len 56
[ 538.284667] DMAR: DRHD: handling fault status reg 2
[ 538.290017] DMAR: [DMA Write] Request device [02:00.4] fault addr f2910000 [fault reason 05] PTE Write access is not set

somehow when crypto_authenc_encrypt() -> scatterwalk_ffwd()-> sg_set_page()

->sg_set_page(dst, sg_page(src), src->length - len, src->offset + len);

src->offset + len gets set as sg->offset in sg_set_page(). Either the
assumption that there should be room is incorrect, or some higher order crypto
code that ends up setting the offset did the wrong calculation.

if src->offset is already towards the end of the page, then offset+len will
go beyond the end of page.


On Wed, Sep 27, 2017 at 09:29:23PM +0000, Casey Leedom wrote:
> Hey Raj,
>
> Let us know if you need help in gathering more debugging information. For
> the time being we've decided to ERRATA the use of the Intel I/O MMU with
> IPsec till we Root Cause the issue. But this is still at the top of Harsh's
> bug list.
>
> With Robin's comments, I'm almost sure that the:
>
> (iov_pfn + sg->offset) << VTD_PAGE_SHIFT)

true, but this is the IOVA- IO Virtual address generated by the
dma_map call. Thought in cases when sg->offset is beyond a page, then
the new iov_pfn should fall on the next page. But we can't randomly adjust
here, unless IOMMU has also allocated IOVA for the page overflow.

Cheers,
Ashok

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