Re: [RFC] block layer support for DMA IOMMU bypass mode II

From: Andi Kleen (
Date: Wed Jul 02 2003 - 12:20:26 EST

On Wed, Jul 02, 2003 at 10:55:10AM -0600, Grant Grundler wrote:
> On Wed, Jul 02, 2003 at 01:57:01AM +0200, Andi Kleen wrote:
> > The K8 IOMMU cannot support this virtually contiguous thing. The reason
> > is that there is no guarantee that an entry in a sglist is a multiple
> > of page size. And the aperture can only map 4K sized chunks, like
> > a CPU MMU. So e.g. when you have an sglist with multiple 1K entries there is
> > no way to get them continuous in IOMMU space (short of copying)
> Can two adjacent IOMMU entries be used to map two 1K buffers?
> Assume the 1st buffer ends on a 4k alignment and the next one
> starts on a 4k alignment.

Yes, it could. But is that situation likely/worth to handle?

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