On Fri, 2012-09-28 at 11:46 +0200, Joerg Roedel wrote: > Even on modern hardware with modern (IOMMU aware) kernels there is still > this small time window when the OS has enabled the IOMMU and the USB > driver is not initialized yet. In this time window the RMRR memory > region is still necessary, no?
Yes but there's no *reason* for that. It wouldn't be that hard to ask the firmware to quiesce all its own DMA *before* we enable the IOMMU. > As I said already in another mail, I think it is safe to ignore any RMRR > requirements when we start to use a device in the OS. I think the whole point in this patch is that there is some brain-dead hardware out there (vendor 'value subtract' I think) on which that common-sense observation isn't actually true. I'm all for handling that broken hardware with quirks, giving clear messages to the user that the device(+firmware) in question is broken, and refusing to let either the kernel *or* VM guests do any DMA with it. -- dwmw2
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