Messages in this thread | | | From | richard.brunner@amd ... | Subject | RE: IOMMUs was Re: Intel vs AMD x86-64 | Date | Tue, 24 Feb 2004 09:50:02 -0600 |
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> -----Original Message----- > From: Andi Kleen [mailto:ak@suse.de]
> On Opteron the IOMMU code (ab)uses the built in AGPv3 GART in > the CPU, which > was originally intended for AGP. AMD converted it to be able > to remap PCI especially for Linux, which I think deserves applause. > > It works surprisingly well even though it was not designed as > a real IOMMU. Of course one of the main advantages of a real > IOMMU - preventing arbitary memory corruption from broken > devices - is lost because the remapping table is just a hole > in the memory. I'm > secretly hoping that when there is more support for Linux at > chipset vendors they will someday add a bit to isolate all > traffic that doesn't go through the GART from the main > memory. This way you could get a much more reliable system > that can tolerate broken PCI devices at a moderate > performance penalty.
Andi is being modest. It was he and Andrea Arcangeli who convinced me we had a problem. We found a way to trick the AGP GART hardware into helping, and then they turned it into a "real" solution and helped us work the warts out of the BIOS to enable it.
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