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

["Raj, Ashok" <ashok.raj@intel.com>]

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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


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Sometimes offset can be greater than 4K. vt-d needs to account for that.

From: Ashok Raj <ashok.raj@intel.com>

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
---
 drivers/iommu/intel-iommu.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 6784a05..d43b566 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2254,10 +2254,13 @@ static int __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
 		uint64_t tmp;
 
 		if (!sg_res) {
+			size_t off = sg->offset & ~VTD_PAGE_SHIFT;
 			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 + sg->offset) << 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 << VTD_PAGE_SHIFT)) | prot;
 			phys_pfn = pteval >> VTD_PAGE_SHIFT;
 		}