[coreboot] DMA protection? [AMD-Vi]

Rudolf Marek r.marek at assembler.cz
Mon Nov 21 19:54:03 CET 2016

Hi all,

Let me jump in. From the OS point of view the BME should be set for:

1) PCI bridges

2) for PCI class of IOAPIC devices (otherwise OS will not get any interrupt!)
This PCI IOAPIC is for example on more high-end Xeons

3) sometimes it needs to be set on internal chipset devices. I remember that if
440BX had clear special cycle cleared it would refuse to poweroff - hard to
debug! I guess per chipset it must be checked if it works with BME off...

4) the rest of the devices should have BME off

Side note:

BME is ignored by Intel integrated graphics - the DMA runs even if the BME is
clear (this happens on core i7 chipsets for example) Thus thatswhy it needs RMRR
IOMMU range for VGA...


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