Re: [PATCH v1] igu_uio: fix IOMMU domain issue

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/11/2016 8:35 AM, Alejandro Lucero wrote:
> On Tue, May 10, 2016 at 4:59 PM, Stephen Hemminger <
> stephen@networkplumber.org> wrote:
> 
>> On Tue, 10 May 2016 19:21:41 +0800
>> Zhe Tao <zhe.tao@intel.com> wrote:
>>
>>> Problem:
>>> The following  operations will cause the igb_uio based DPDK
>>> operation failed.
>>> --Any device assignment through the kvm_assign_device interface,
>>> this can be the pci-assign method in QEMU
>>> --VFIO group attachment operation(attach to the container)
>>> this can happens in  vfio-pci assignment in QEMU
>>
>>
>> If you have an IOMMU why not use VFIO instead, it is better.
>>
> 
> It is not about VFIO against UIO but about how iommu domains are created
> and destroyed by the (old) kernel when iommu=pt. So even with VFIO you can
> have problems.

Problem is in IOMMU driver but we are adding a workaround to igb_uio, if
using VFIO solves the issue, I believe that is better workaround.

1) Is there any case IOMMU supported but VFIO is not supported? Is there
anything forces to use igb_uio?

2) Does using VFIO solves the issue defined in problem statement?

> 
> We have had problems like this and other due to our device (NFP) just
> mapping up to 40 bits of address space. Old kernels used in LTS
> distributions like Ubuntu are iommu buggy and you need to do things like
> this mapping inside the driver for solving problems. By the way, using
> SRIOV just adds more problems. It is not safe to use iommu=pt with 3.13.x
> Ubuntu kernels.
> 
> It would be a good thing for the original patch to identify those kernels
> where the problem was detected. Of course, there could be more kernels with
> the same problem but that is more work to do.
> 

Thanks,
ferruh