Re: [PATCH 0/8] Passthrough support for AMD-IOMMU (AMD-Vi)

From: David Woodhouse
Date: Mon Sep 07 2009 - 08:54:41 EST

On Fri, 2009-09-04 at 11:36 +0200, Joerg Roedel wrote:
> this series of patches implement iommu=pt support for AMD IOMMU (AMD-Vi). If
> this option is passed on the kernel command line, the AMD-Vi driver will not
> register itself as the dma_ops backend and allows all devices unlimited access
> to main memory as long as no other kernel part (currently only KVM will do so)
> assigns the device to another domain using the IOMMU-API.

The Intel IOMMU used to behave like that in passthrough mode, but I've
now changed it. Now, it will still register itself as the dma_ops
backend, and it won't actually bypass the IOMMU for devices with a
limited dma_mask. So you don't end up having to use swiotlb for those
(which wasn't working anyway, iirc).

The devices for which you actually care about performance are still
going to end up with the passthrough mapping as you desire, anyway.

David Woodhouse Open Source Technology Centre
David.Woodhouse@xxxxxxxxx Intel Corporation

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