Hi Christoph,
On 4/26/19 11:04 PM, Christoph Hellwig wrote:
On Thu, Apr 25, 2019 at 10:07:19AM +0800, Lu Baolu wrote:
This is not VT-d specific. It's just how generic IOMMU works.
Normally, IOMMU works in paging mode. So if a driver issues DMA with
IOVA 0xAAAA0123, IOMMU can remap it with a physical address 0xBBBB0123.
But we should never expect IOMMU to remap 0xAAAA0123 with physical
address of 0xBBBB0000. That's the reason why I said that IOMMU will not
work there.
Well, with the iommu it doesn't happen. With swiotlb it obviosuly
can happen, so drivers are fine with it. Why would that suddenly
become an issue when swiotlb is called from the iommu code?
I would say IOMMU is DMA remapping, not DMA engine. :-)
Best regards,
Lu Baolu
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