Messages in this thread | | | Subject | Re: [PATCH 00/21] Control VQ support in vDPA | From | Jason Wang <> | Date | Fri, 18 Dec 2020 10:56:34 +0800 |
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On 2020/12/18 上午6:28, Michael S. Tsirkin wrote: > On Thu, Dec 17, 2020 at 05:02:49PM +0800, Jason Wang wrote: >> On 2020/12/17 下午3:58, Michael S. Tsirkin wrote: >>> On Thu, Dec 17, 2020 at 11:30:18AM +0800, Jason Wang wrote: >>>> On 2020/12/16 下午5:47, Michael S. Tsirkin wrote: >>>>> On Wed, Dec 16, 2020 at 02:47:57PM +0800, Jason Wang wrote: >>>>>> Hi All: >>>>>> >>>>>> This series tries to add the support for control virtqueue in vDPA. >>>>>> >>>>>> Control virtqueue is used by networking device for accepting various >>>>>> commands from the driver. It's a must to support multiqueue and other >>>>>> configurations. >>>>>> >>>>>> When used by vhost-vDPA bus driver for VM, the control virtqueue >>>>>> should be shadowed via userspace VMM (Qemu) instead of being assigned >>>>>> directly to Guest. This is because Qemu needs to know the device state >>>>>> in order to start and stop device correctly (e.g for Live Migration). >>>>>> >>>>>> This requies to isolate the memory mapping for control virtqueue >>>>>> presented by vhost-vDPA to prevent guest from accesing it directly. >>>>>> To achieve this, vDPA introduce two new abstractions: >>>>>> >>>>>> - address space: identified through address space id (ASID) and a set >>>>>> of memory mapping in maintained >>>>>> - virtqueue group: the minimal set of virtqueues that must share an >>>>>> address space >>>>> How will this support the pretty common case where control vq >>>>> is programmed by the kernel through the PF, and others by the VFs? >>>> In this case, the VF parent need to provide a software control vq and decode >>>> the command then send them to VF. >>> But how does that tie to the address space infrastructure? >> In this case, address space is not a must. > That's ok, problem is I don't see how address space is going > to work in this case at all. > > There's no address space there that userspace/guest can control. >
The virtqueue group is mandated by parent but the association between virtqueue group and address space is under the control of userspace (Qemu).
A simple but common case is that:
1) Device advertise two virtqueue groups: group 0 contains RX and TX, group 1 contains CVQ. 2) Device advertise two address spaces
Then, for vhost-vDPA using by VM:
1) associate group 0 with as 0, group 1 with as 1 (via vhost-vDPA VHOST_VDPA_SET_GROUP_ASID) 2) Publish guest memory mapping via IOTLB asid 0 3) Publish control virtqueue mapping via IOTLB asid 1
Then the DMA is totally isolated in this case.
For vhost-vDPA using by DPDK or virtio-vDPA
1) associate group 0 and group 1 with as 0
since we don't need DMA isolation in this case.
In order to let it be controlled by Guest, we need extend virtio spec to support those concepts.
Thanks
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