Re: [Qemu-devel] Assigning an eth port to a guest VM

[Eric Auger <eric.auger@linaro.org>]

Hi Yehuda,
On 06/15/2015 06:52 PM, Yehuda Yitschak wrote:
> 
> ________________________________________
> From: Eric Auger <eric.auger@linaro.org>
> Sent: Monday, June 15, 2015 4:42 PM
> To: Yehuda Yitschak; qemu-devel@nongnu.org
> Cc: Yuval Caduri; Shadi Ammouri
> Subject: Re: Assigning an eth port to a guest VM
> 
> Hi Yehuda,
> On 06/15/2015 01:01 PM, Yehuda Yitschak wrote:
>>> Cc: Eric Auger
>>>
>>>> -----Original Message-----
>>>> From: Yehuda Yitschak
>>>> Sent: Monday, June 15, 2015 9:35
>>>> To: qemu-devel@nongnu.org
>>>> Cc: Yuval Caduri; Shadi Ammouri
>>>> Subject: Assigning an eth port to a guest VM
>>>>
>>>> Hello
>>>>
>>>> I would to ask your advice on how to assign a semi-virtualized Ethernet port
>>>> to a guest VM
>>>>
>>>> The eth port's HW partially supports virtualization since the data path MMIO
>>>> registers (which controls rx/tx operation) are duplicated per VM.
>>>> So for the run-time operation the guest can directly access the MMIO
>>>> registers, using VFIO-PLATFORM, and enjoy the performance benefit.
>>>>
>>>> However for the initial setup and occasional configuration the guest need to
>>>> access control path registers which are shared for all guests.
>>>> AFAIK this is usually done with HW emulation using trap & emulate with
>>>> QEMU.
>>>> So, to the best of my knowledge I need a mix of VFIO and HW emulation to
>>>> get the port to work with device assignment , right ?
>> Yes to me you're correct.
>>>>
>>>> Are there any standard methods for achieving this ?
>>>> Is there an example for such an existing HW in QEMU ?
>> Not yet unfortunately. To my knowledge the only platform devices that
>> were assigned with QEMU VFIO platform were standalone duplicated
>> devices, PL330, Calxeda Xgmac, SATA. So you are a trailblazer on that
>> track.
> 
> Thanks. It's good to know the diagnosis :-)
> 
> BTW - i thought SR-IOV uses a somewhat similar concept. AFAIK each virtual function (VF) gets 
> a set of registers enabling it to perform data path but most of the configuration and management
> operations are controlled by the host using the Physical Function PF driver. 
> Are you familiar with that ?
I have the same understanding about PCI SR-IOV but unfortunately I am
not sufficiently familiar with it to give you any advice.

> i know SR-IOV is not related to VFIO-PLATFORM but if the mixed of direct access and emulation
> exists there as well then maybe i can borrow some concepts 

I hope so. I am also interested in the topic!

Best Regards

Eric


> 
> Best regards
> 
> Yehuda
>  
>> Best Regards
>>
>> Eric
>>>>
>>>> Thanks
>>>>
>>>> Yehuda Yitschak