This is a bit tricky, since AMD laid off the team who were maintaining
this, but I added to the cc' one of the original maintainers in the
hopes they can take a look.
James
On Tue, 2013-02-19 at 18:30 -0800, Eddie Wai wrote:
> Hello,
>
> For a 64-bit DMA capable PCIe storage HBA running under the 64-bit
> AMD-VI IOMMU environment, the amd_iommu code was observed to hit an
> overflow when it tries to page align the dma_parms->segment_boundary_mask.
> This overflow would eventually trigger the BUG_ON in the iommu-helper's
> iommu_is_span_boundary is_power_of_2 check.
>
> A little back tracking shows that since the device is 64-bit DMA capable,
> the pcidev->dma_mask was correctly set to DMA_BIT_MASK(64). This dma_mask
> was then transferred to the SCSI host's dma_boundary param (by the iSCSI
> driver) and was eventually used to populate the q->limits.seg_boundary_mask
> (via blk_queue_segment_boundary) and the dma_parms->segment_boundary_mask
> (via dma_set_seg_boundary) during the scsi queue allocation.
>
> The code seems correct as it make sense to impose the same hardware
> segment boundary limit on both the blk queue and the DMA code. It would
> be an easy alternative to simply prevent the shost->dma_boundary from
> being set to DMA_BIT_MASK(64), but it seems more correct to fix the
> amd_iommu code itself to detect and handle this max 64-bit mask condition.
>
> Please let me know your comments.
>
> Thanks,
> Eddie
>
> Signed-off-by: Eddie Wai <eddie.wai@xxxxxxxxxxxx>
> ---
> drivers/iommu/amd_iommu.c | 7 +++++--
> 1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> index d90a421..63185a1 100644
> --- a/drivers/iommu/amd_iommu.c
> +++ b/drivers/iommu/amd_iommu.c
> @@ -1526,11 +1526,14 @@ static unsigned long dma_ops_area_alloc(struct device *dev,
> unsigned long boundary_size;
> unsigned long address = -1;
> unsigned long limit;
> + unsigned long mask;
>
> next_bit >>= PAGE_SHIFT;
>
> - boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
> - PAGE_SIZE) >> PAGE_SHIFT;
> + mask = dma_get_seg_boundary(dev);
> + boundary_size = mask + 1 ?
> + ALIGN(mask + 1, PAGE_SIZE) >> PAGE_SHIFT :
> + 1UL << (BITS_PER_LONG - PAGE_SHIFT);
>
> for (;i < max_index; ++i) {
> unsigned long offset = dom->aperture[i]->offset >> PAGE_SHIFT;
--
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