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

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Date:   Thu, 28 Sep 2017 19:08:21 +0530
From:   Harsh Jain <Harsh@...lsio.com>
To:     Casey Leedom <leedom@...lsio.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     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 02:59, 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)
>
> in your suggested patch is an issue.  iov_pfn is a Page Frame Number and
> sg->offset is a Byte Offset.  It feels like this should be:
>
>     size_t page_off = sg->offset & ~VTD_PAGE_MASK;
>     unsigned long pfn_off = sg->offset >> VTD_PAGE_MASK;
>     ...
>     sg->dma_address = ((dma_addr_t)
>                        (iov_pfn + pfn_off) << VTD_PAGE_SHIFT) + page_off;
>
> When Harsh tried your original patch, Harsh' test system wouldn't even boot.
Today I tried with "Intel_iommu=sp_off" boot option. Traffic runs without any error for more than 1 hrs. What magic this option did? :)
>
> Casey