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

From: Andi Kleen (
Date: Tue Jul 01 2003 - 19:22:44 EST

On Tue, 01 Jul 2003 17:03:23 -0700 (PDT)
"David S. Miller" <> wrote:

> From: Andi Kleen <>
> Date: Wed, 2 Jul 2003 01:57:01 +0200
> 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
> What do you mean? You map only one 4K chunk, and this is used
> for all the sub-1K mappings.

How should this work when the 1K mappings are spread all over memory?

Maybe I'm missing something but from James description it sounds like the
block layer assumes that it can pass in a sglist with arbitary elements
and get it back remapped to continuous DMA addresses.

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