On Fri, Sep 28, 2012 at 11:23:23AM +0100, David Woodhouse wrote: > 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.
True. That would have been a better approach. Some kind of IOMMU handover from firmware to the OS. > > 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. Well, it is probably mostly about southbridge devices and add-on USB controllers. Or is there any other way a given device can communicate RMRR requirements to the firmware? Anyway, I am fine with completly blocking DMA for those devices too. Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu