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

[Herbert Xu]

On Wed, Sep 27, 2017 at 10:13:04PM +0000, Casey Leedom wrote:
> | From: Raj, Ashok <ashok.raj@xxxxxxxxx>
> | Sent: Wednesday, September 27, 2017 12:07 PM
> |
> | 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.
> 
>   Hhmmm, it seems like we need Herbert to comment on this.
> 
>   Herbert, is there any specific debugging information that you'd like to
> see here?

OK I was mistaken.  While SG lists can contain entries that are
larger than PAGE_SIZE, there is no reason why scatterwalk_ffwd
should gratuitously insert a page_offset that is greater than
PAGE_SIZE.

Harsh, can you please submit your original patch with a sign-off?

Thanks,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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