Integrated MegaRAID controller and AMD IOMMU issue

Integrated MegaRAID controller and AMD IOMMU issue

[James Georgas]

I have a Supermicro H8DG6-F board, which has an LSI  SAS2008 RAID controller on it with the optional RAID5 hardware key installed. I have set up a three disk RAID5 array, using the LSI WebBIOS utility.

My kernel is configured with the MEGARAID_SAS driver. The driver picks up the RAID5 array, and I can read and write it with no problems. (In fact, my root filesystem is on a JBOD disk attached to the same controller, and I have no problems with it). However, as soon as I enable the AMD IOMMU in the kernel, bad things start to happen. The driver still picks up the RAID5 array, but any attempt to access it causes the machine to become non-responsive, and I have recover via hard reset.

I discussed the issue with an LSI engineer, and he said that since the integrated controller uses system memory, which it gets from the BIOS during initialization, there will be issues with the IOMMU. I assume he is referring to DMA address problems due to IOMMU translation.

My question is: is this something that can be addressed in the kernel drivers (MEGARAID_SAS or AMD_IOMMU), for example by protecting the LSI controller's memory resources from the IOMMU, or am I just out of luck here?

Cheers,
	James

Re: Integrated MegaRAID controller and AMD IOMMU issue

[Joerg Roedel]

Hi James,

On Tue, Jun 25, 2013 at 12:12:53AM -0600, James Georgas wrote:
> I discussed the issue with an LSI engineer, and he said that since the
> integrated controller uses system memory, which it gets from the BIOS
> during initialization, there will be issues with the IOMMU. I assume
> he is referring to DMA address problems due to IOMMU translation.

Looks like the problem is in the LSI driver. The driver needs to dma-map
the system memory it gets from the BIOS (for example with dma_map_single)
and use the dma_handle returned for transactions. Otherwise the IOMMU
will block the accesses from the device and make it unusable.


	Joerg