Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Re: [RFC] block layer support for DMA IOMMU bypass mode | Date | 1 Jul 2003 10:54:31 -0700 |
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Followup to: <1057080529.2003.62.camel@mulgrave> By author: James Bottomley <James.Bottomley@steeleye.com> In newsgroup: linux.dev.kernel > > The name was simply to be consistent with BIO_VMERGE_BOUNDARY which is > another asm/io.h setting for this. > > Could you elaborate more on the amd64 IOMMU window. Is this a window > where IOMMU mapping always takes place? >
It's a window (in the form of a BAR - base and mask) within which IOMMU mapping always takes place. Outside the window everything is bypass.
This applies to all x86-64 machines and some i386 machines, in particular those i386 chipsets with "full GART" support as opposed to "AGP only GART" (my terminology.)
Andi likes to say this isn't a real IOMMU (mostly because it doesn't solve the legacy region problem), but I disagree with that view. It still would be nicer if it covered more address space, though.
I don't know if it would be worthwhile to support "full GART" on the i386 systems which support it.
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