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

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Message-ID: <0764911a-1412-4a42-cf6b-74c6b78a4c3f@chelsio.com>
Date:   Thu, 28 Sep 2017 10:31:35 +0530
From:   Harsh Jain <Harsh@...lsio.com>
To:     Casey Leedom <leedom@...lsio.com>,
        "Raj, Ashok" <ashok.raj@...el.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "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>,
        Michael Werner <werner@...lsio.com>, "nd@....com" <nd@....com>
Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in
 Intel IOMMU


On 28-09-2017 03:43, Casey Leedom wrote:
> | From: Raj, Ashok <ashok.raj@...el.com>
> | 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
Input received from user(Here XFRM) contains AAD(Additional Authentication data) || DATA(enc/dec) || Tag(hash). before passing input
to Cipher engine(chelsio) crypto_authenc_encrypt has to skip AAD which is 16 in our case. To skip that 16 bytes they simply incremented offset by 16. 
I think Robin is right DMA mapping should handle it.
> | 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?
>
> Casey