[dpdk-dev] vhost compliant virtio based networking interface in container

Xie, Huawei huawei.xie at intel.com
Tue Aug 25 11:56:59 CEST 2015

On 8/25/2015 10:59 AM, Tetsuya Mukawa wrote:
> Hi Xie and Yanping,
> May I ask you some questions?
> It seems we are also developing an almost same one.

Good to know that we are tackling the same problem and have the similar
What is your status now? We had the POC running, and compliant with
Interrupt like notification isn't supported.

> On 2015/08/20 19:14, Xie, Huawei wrote:
>> Added dev at dpdk.org
>> On 8/20/2015 6:04 PM, Xie, Huawei wrote:
>>> Yanping:
>>> I read your mail, seems what we did are quite similar. Here i wrote a
>>> quick mail to describe our design. Let me know if it is the same thing.
>>> Problem Statement:
>>> We don't have a high performance networking interface in container for
>>> NFV. Current veth pair based interface couldn't be easily accelerated.
>>> The key components involved:
>>>     1.    DPDK based virtio PMD driver in container.
>>>     2.    device simulation framework in container.
>>>     3.    dpdk(or kernel) vhost running in host.
>>> How virtio is created?
>>> A:  There is no "real" virtio-pci device in container environment.
>>> 1). Host maintains pools of memories, and shares memory to container.
>>> This could be accomplished through host share a huge page file to container.
>>> 2). Containers creates virtio rings based on the shared memory.
>>> 3). Container creates mbuf memory pools on the shared memory.
>>> 4) Container send the memory and vring information to vhost through
>>> vhost message. This could be done either through ioctl call or vhost
>>> user message.
>>> How vhost message is sent?
>>> A: There are two alternative ways to do this.
>>> 1) The customized virtio PMD is responsible for all the vring creation,
>>> and vhost message sending.
> Above is our approach so far.
> It seems Yanping also takes this kind of approach.
> We are using vhost-user functionality instead of using the vhost-net
> kernel module.
> Probably this is the difference between Yanping and us.

In my current implementation, the device simulation layer talks to "user
space" vhost through cuse interface. It could also be done through vhost
user socket. This isn't the key point.
Here vhost-user is kind of confusing, maybe user space vhost is more
accurate, either cuse or unix domain socket. :).

As for yanping, they are now connecting to vhost-net kernel module, but
they are also trying to connect to "user space" vhost.  Correct me if wrong.
Yes, there is some difference between these two. Vhost-net kernel module
could directly access other process's memory, while using
vhost-user(cuse/user), we need do the memory mapping.
> BTW, we are going to submit a vhost PMD for DPDK-2.2.
> This PMD is implemented on librte_vhost.
> It allows DPDK application to handle a vhost-user(cuse) backend as a
> normal NIC port.
> This PMD should work with both Xie and Yanping approach.
> (In the case of Yanping approach, we may need vhost-cuse)
>>> 2) We could do this through a lightweight device simulation framework.
>>>     The device simulation creates simple PCI bus. On the PCI bus,
>>> virtio-net PCI devices are created. The device simulations provides
>>> IOAPI for MMIO/IO access.
> Does it mean you implemented a kernel module?
> If so, do you still need vhost-cuse functionality to handle vhost
> messages n userspace?

The device simulation is  a library running in user space in container. 
It is linked with DPDK app. It creates pseudo buses and virtio-net PCI
The virtio-container-PMD configures the virtio-net pseudo devices
through IOAPI provided by the device simulation rather than IO
instructions as in KVM.
Why we use device simulation?
We could create other virtio devices in container, and provide an common
way to talk to vhost-xx module.

>>>    2.1  virtio PMD configures the pseudo virtio device as how it does in
>>> KVM guest enviroment.
>>>    2.2  Rather than using io instruction, virtio PMD uses IOAPI for IO
>>> operation on the virtio-net PCI device.
>>>    2.3  The device simulation is responsible for device state machine
>>> simulation.
>>>    2.4   The device simulation is responsbile for talking to vhost.
>>>      With this approach, we could minimize the virtio PMD modifications.
>>> The virtio PMD is like configuring a real virtio-net PCI device.
>>> Memory mapping?
>>> A: QEMU could access the whole guest memory in KVM enviroment. We need
>>> to fill the gap.
>>> container maps the shared memory to container's virtual address space
>>> and host maps it to host's virtual address space. There is a fixed
>>> offset mapping.
>>> Container creates shared vring based on the memory. Container also
>>> creates mbuf memory pool based on the shared memroy.
>>> In VHOST_SET_MEMORY_TABLE message, we send the memory mapping
>>> information for the shared memory. As we require mbuf pool created on
>>> the shared memory, and buffers are allcoated from the mbuf pools, dpdk
>>> vhost could translate the GPA in vring desc to host virtual.
>>> GPA or CVA in vring desc?
>>> To ease the memory translation, rather than using GPA, here we use
>>> CVA(container virtual address). This the tricky thing here.
>>> 1) virtio PMD writes vring's VFN rather than PFN to PFN register through
>>> IOAPI.
>>> 2) device simulation framework will use VFN as PFN.
>>> 3) device simulation sends SET_VRING_ADDR with CVA.
>>> 4) virtio PMD fills vring desc with CVA of the mbuf data pointer rather
>>> than GPA.
>>> So when host sees the CVA, it could translates it to HVA(host virtual
>>> address).
>>> Worth to note:
>>> The virtio interface in container follows the vhost message format, and
>>> is compliant with dpdk vhost implmentation, i.e, no dpdk vhost
>>> modification is needed.
>>> vHost isn't aware whether the incoming virtio comes from KVM guest or
>>> container.
>>> The pretty much covers the high level design. There are quite some low
>>> level issues. For example, 32bit PFN is enough for KVM guest, since we
>>> use 64bit VFN(virtual page frame number),  trick is done here through a
>>> special IOAPI.
> In addition above, we might consider "namespace" kernel functionality.
> Technically, it would not be a big problem, but related with security.
> So it would be nice to take account.

There is no namespace concept here because we don't generate kernel
netdev devices. It might be usefull if we could extend our work to
support kernel netdev interface and assign to container's namespace.

> Regards,
> Tetsuya
>>> /huawei

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