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

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Date:   Tue, 26 Sep 2017 07:34:41 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Harsh Jain <Harsh@...lsio.com>, Casey Leedom <leedom@...lsio.com>,
        Herbert Xuy <herbert@...dor.apana.org.au>,
        David Woodhouse <David.Woodhouse@...el.com>,
        "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>,
        Dan Williams <dan.j.williams@...el.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in
 Intel IOMMU

On Tue, Sep 26, 2017 at 03:22:47PM +0100, Robin Murphy wrote:
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 6784a05dd6b2..d7f7def81613 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2254,10 +2254,12 @@ static int __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
>  		uint64_t tmp;
>  
>  		if (!sg_res) {
> +			size_t off = sg->offset & ~PAGE_MASK;

Should this be VTD_PAGE_MASK?

> +
>  			sg_res = aligned_nrpages(sg->offset, sg->length);
> -			sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + sg->offset;
> +			sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + off;
>  			sg->dma_length = sg->length;
> -			pteval = page_to_phys(sg_page(sg)) | prot;
> +			pteval = (page_to_phys(sg_page(sg)) + sg->offset - off) | prot;

Something seems wrong here.. sg->offset can be > VTD_PAGE_SIZE, think 
we should add sg->offset and then find the pteval?

attached below another cut at fixing the same problem.. if there is something
obvious i missed, let me know.

again.. untested :-)

Cheers,
Ashok


View attachment "fix-vtd-offset-gt4k" of type "text/plain" (1050 bytes)