Messages in this thread | | | Date | Thu, 20 Nov 2008 08:51:39 +0100 | From | Ingo Molnar <> | Subject | Re: [GIT PULL] AMD IOMMU updates for 2.6.28-rc5 |
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* FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:
> > > It had been the default option for AMD IOMMU until you hit the > > > bugs. IIRC, VT-d also shares a protection domain by default. It > > > would be nice to avoid surprising users if the two > > > virtualization IOMMUs works in the similar way. > > > > Calgary has a per-bus protection domain, both on x86 and PPC. > > I see. Then it might be better to change VT-d to use a separate > protection domain by default.
yes, agreed, and that should be the sane default for any IOMMU driver - unless the performance impact is prohibitive.
Note that this widens the positive impact of the IOMMU code: not only does it enable transparent support of DMA to/from devices that have a limited DMA range, not only does it help isolation in virtualization - it also acts as a daily debug helper for _native_ drivers.
Note that people will prefer to run with an IOMMU enabled even if all devices support the full memory range - just due to the DMA protection features. Just like people prefer to run an OS with paging protections enabled ;-)
It also puts pressure on the hw design side to treat IOMMUs not just as some fringe feature for compatibility with older transports or virtualization, but also as a prime-time native IO feature.
Ingo
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