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

From: Yehuda Yitschak <yehuday@marvell.com>
To: Eric Auger <eric.auger@linaro.org>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	Shadi Ammouri <shadi@marvell.com>,
	Yuval Caduri <cyuval@marvell.com>
Subject: Re: [Qemu-devel] Assigning an eth port to a guest VM
Date: Mon, 15 Jun 2015 16:52:15 +0000	[thread overview]
Message-ID: <1434387134955.13544@marvell.com> (raw)
In-Reply-To: <557ED62A.8050409@linaro.org>

________________________________________
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 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 

Best regards

Yehuda

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