[dpdk-dev] IXGBE, IOMMU DMAR DRHD handling fault issue

[Burakov, Anatoly]

On 06-Feb-18 5:55 PM, Ravi Kerur wrote:
> 
> Hi Anatoly,
> 
> I am actually confused with the state of vIOMMU + DPDK. Can you please 
> help me clarify?
> 
> I tested following DPDK versions
> 
> (1) DPDK 17.11, exhibits the issue (IOMMU width as reported by RedHat 
> and solution is to prevent using the patch)
> (2) DPDK 17.05.02 (stable release) using 'testpmd' I was able to bind a 
> device in VM with VFIO driver and no DMAR error message on host
> (3) DPDK 16.11.02 (stable release) using 'testpmd' I was able to bind a 
> device in VM with VFIO driver and no DMAR error message on host
> 
> Clearly issue seen in 17.11 without the patch you mentioned is a 
> regression or the issue was masked in earlier DPDK version?  I did not 
> test traffic with any DPDK version because I wanted to first get DMAR 
> errors on host gone.
> 
> Our application 'v1' is integrated with DPDK 16.11 and 'v2' is 
> integrated with DPDK 17.05.01. In both 'v1' and 'v2' cases I don't see 
> IOMMU width error messages on VM, however, DMAR error messages are seen 
> host. I am not able to relate what causes DMAR error messages on host?
> 
> 
> Thanks.
> 

Hi Ravi,

vIOMMU support is out of our hands, really - we can only make use of 
hardware (or emulation of it) that is available. 39-bit wide address 
*can* work, you just have to be lucky and get PA addresses that would 
fit into 39 bits (so under 512G limit), because we set up IOVA addresses 
to be 1:1 to physical addresses. We could, in principle, set up IOVA 
addresses to go from zero instead of them being a 1:1 mapping to 
physical addresses, but that would introduce need to translate addresses 
between IOVA and physical in some cases (e.g. KNI).

I'm not aware of any changes between 16.11 and 17.11 (and indeed 18.02) 
that would make or break support for 39-bit wide PA addresses for IOMMU. 
It is possible that VF/PF drivers do something differently which results 
in DMAR errors showing up sooner rather than later, but as far as VFIO 
support itself is concerned, there were no major changes in those releases.

-- 
Thanks,
Anatoly