[dpdk-dev] Query : Does Binding with vfio-pci is supported inside qemu-kvm guest/vm instance.?

[Ilya Maximets]

> On 12-Mar-19 10:20 AM, Bruce Richardson wrote:
>> On Tue, Mar 12, 2019 at 05:54:39PM +0800, Jason Wang wrote:
>>>
>>> On 2019/3/12 下午5:42, Thanneeru Srinivasulu wrote:
>>>> Thanks Bruce..
>>>>
>>>> On Tue, Mar 12, 2019 at 3:08 PM Bruce Richardson
>>>> <bruce.richardson at intel.com> wrote:
>>>>> On Tue, Mar 12, 2019 at 10:57:55AM +0530, Thanneeru Srinivasulu wrote:
>>>>>> Hi Everyone.
>>>>>>
>>>>>> I did attached pice  to Guest VM using vfio-pci with qemu command, and then
>>>>>> tried binding the pcie bdf with vfio-pci, observing binding failure with
>>>>>> vfio-pci.
>>>>>>
>>>>>> Where as when tryied with igb_uio, everything works fine.
>>>>>>
>>>>>> Does Binding with vfio-pci is supported inside VM/guest?
>>>>>>
>>>>> vfio support requires the presence of an IOMMU, and you generally don't
>>>>> have an IOMMU available in a VM.
>>>>>
>>>>> /Bruce
>>>
>>>
>>> Actually, Qemu support vIOMMU + VFIO in guest[1], all you need is to add a
>>> intel IOMMU and enabling caching mode.
>>>
>>> Thanks
>>>
>>>
>>> [1]
>>>
>>> https://www.lfasiallc.com/wp-content/uploads/2017/11/Device-Assignment-with-Nested-Guests-and-DPDK_Peter-Xu.pdf
>>>
>> Thanks for the info.
>> 
>> /Bruce
>> 
> 
> One more thing: even without vIOMMU, VFIO has no-IOMMU mode which can be 
> enabled (for a recent-enough kernel). This will make VFIO work even in 
> cases where the guest doesn't have IOMMU emulation. See? There's no 
> reason to use igb_uio, ever! :D

Agree.

You could use following commands to enable no-IOMMU mode:

  modprobe vfio-pci
  echo 1 > /sys/module/vfio/parameters/enable_unsafe_noiommu_mode

This should allow using vfio-pci driver without IOMMU emulation.
However, there will be no any security accordingly.

Best regards, Ilya Maximets.

> 
> -- 
> Thanks,
> Anatoly
>