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Date:   Tue, 12 Jan 2021 11:11:53 +0800
From:   Jason Wang <>
To:     Eli Cohen <>
Subject: Re: [PATCH 21/21] vdpasim: control virtqueue support

On 2021/1/11 下午8:26, Eli Cohen wrote:
> On Wed, Dec 16, 2020 at 02:48:18PM +0800, Jason Wang wrote:
>> This patch introduces the control virtqueue support for vDPA
>> simulator. This is a requirement for supporting advanced features like
>> multiqueue.
>> A requirement for control virtqueue is to isolate its memory access
>> from the rx/tx virtqueues. This is because when using vDPA device
>> for VM, the control virqueue is not directly assigned to VM. Userspace
>> (Qemu) will present a shadow control virtqueue to control for
>> recording the device states.
>> The isolation is done via the virtqueue groups and ASID support in
>> vDPA through vhost-vdpa. The simulator is extended to have:
>> 1) three virtqueues: RXVQ, TXVQ and CVQ (control virtqueue)
>> 2) two virtqueue groups: group 0 contains RXVQ and TXVQ; group 1
>>     contains CVQ
>> 3) two address spaces and the simulator simply implements the address
>>     spaces by mapping it 1:1 to IOTLB.
>> For the VM use cases, userspace(Qemu) may set AS 0 to group 0 and AS 1
>> to group 1. So we have:
>> 1) The IOTLB for virtqueue group 0 contains the mappings of guest, so
>>     RX and TX can be assigned to guest directly.
>> 2) The IOTLB for virtqueue group 1 contains the mappings of CVQ which
>>     is the buffers that allocated and managed by VMM only. So CVQ of
>>     vhost-vdpa is visible to VMM only. And Guest can not access the CVQ
>>     of vhost-vdpa.
>> For the other use cases, since AS 0 is associated to all virtqueue
>> groups by default. All virtqueues share the same mapping by default.
>> To demonstrate the function, VIRITO_NET_F_CTRL_MACADDR is
>> implemented in the simulator for the driver to set mac address.
> Hi Jason,
> is there any version of qemu/libvirt available that I can see the
> control virtqueue working in action?

Not yet, the qemu part depends on the shadow virtqueue work of Eugenio. 
But it will work as:

1) qemu will use a separated address space for the control virtqueue 
(shadow) exposed through vhost-vDPA
2) the commands sent through control virtqueue by guest driver will 
intercept by qemu
3) Qemu will send those commands to the shadow control virtqueue

Eugenio, any ETA for the new version of shadow virtqueue support in Qemu?



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