[vfio-users] intel_iommu=on and aacraid / Adaptec 3805

[Alex Williamson]

On Sun, 10 Jul 2016 13:17:41 -0500
David <david283 at gmail.com> wrote:

> I have run into a strange problem, while setting up my Fedora 24 box for
> KVM, i noticed that my raid array stopped showing as an available drive.
> After a lot of troubleshooting and reinstalling linux to this PC 2 more
> times, i have narrowed it down to one setting in my GRUB config.
>  intel_iommu=on
> 
> Just taking that one setting out and rebuilding my grub2-efi.cfg will make
> the array readable again.  When IOMMU is on, the system can see that there
> is a raid card and array, but it lists the partition table as unknown.  It
> also will not successfully create a new GPT partition table on the array.
> With IOMMU off, it can read the partition table and partition fine, read
> and write data, and everything works fine.
> 
> My raid is 4 1TB disks in Raid 10e, GPT partition formatted NTFS.
> 
> $ lspci -v -s 03:0e.0
> 03:0e.0 RAID bus controller: Adaptec AAC-RAID
>     Subsystem: Adaptec 3805
>     Flags: bus master, stepping, 66MHz, medium devsel, latency 32, IRQ 57
>     Memory at fa600000 (64-bit, non-prefetchable) [size=2M]
>     Expansion ROM at fa800000 [disabled] [size=256K]
>     Capabilities: <access denied>
>     Kernel driver in use: aacraid
>     Kernel modules: aacraid


No DMAR faults in dmesg?  There's a fair chance this is one of those
devices that does DMA with the wrong requester ID and therefore
enabling the IOMMU prevents it from working.  We have a mechanism in
the kernel to handle such DMA aliasing if you can verify the issue.
Thanks,

Alex