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

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Date:   Wed, 27 Sep 2017 22:13:04 +0000
From:   Casey Leedom <leedom@...lsio.com>
To:     "Raj, Ashok" <ashok.raj@...el.com>
CC:     Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Harsh Jain" <Harsh@...lsio.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

| 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
| 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