Re: [PATCH v2] Intel IOMMU patch to reprocess RMRR info

[David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

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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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