On 2020/10/20 下午3:39, Yongji Xie wrote:
On Tue, Oct 20, 2020 at 11:20 AM Jason Wang <jasowang@xxxxxxxxxx
<mailto:jasowang@xxxxxxxxxx>> wrote:
On 2020/10/19 下午10:56, Xie Yongji wrote:
> This series introduces a framework, which can be used to implement
> vDPA Devices in a userspace program. To implement it, the work
> consist of two parts: control path emulating and data path
offloading.
>
> In the control path, the VDUSE driver will make use of message
> mechnism to forward the actions (get/set features, get/st status,
> get/set config space and set virtqueue states) from virtio-vdpa
> driver to userspace. Userspace can use read()/write() to
> receive/reply to those control messages.
>
> In the data path, the VDUSE driver implements a MMU-based
> on-chip IOMMU driver which supports both direct mapping and
> indirect mapping with bounce buffer. Then userspace can access
> those iova space via mmap(). Besides, eventfd mechnism is used to
> trigger interrupts and forward virtqueue kicks.
This is pretty interesting!
For vhost-vdpa, it should work, but for virtio-vdpa, I think we
should
carefully deal with the IOMMU/DMA ops stuffs.
I notice that neither dma_map nor set_map is implemented in
vduse_vdpa_config_ops, this means you want to let vhost-vDPA to deal
with IOMMU domains stuffs. Any reason for doing that?
Actually, this series only focus on virtio-vdpa case now. To support
vhost-vdpa, as you said, we need to implement dma_map/dma_unmap. But
there is a limit that vm's memory can't be anonymous pages which are
forbidden in vm_insert_page(). Maybe we need to add some limits on
vhost-vdpa?
I'm not sure I get this, any reason that you want to use
vm_insert_page() to VM's memory. Or do you mean you want to implement
some kind of zero-copy?
I guess from the software device implemention in user space it only need
to receive IOVA ranges and map them in its own address space.
The reason for the questions are:
1) You've implemented a on-chip IOMMU driver but don't expose it to
generic IOMMU layer (or generic IOMMU layer may need some
extension to
support this)
2) We will probably remove the IOMMU domain management in vhost-vDPA,
and move it to the device(parent).
So if it's possible, please implement either set_map() or
dma_map()/dma_unmap(), this may align with our future goal and may
speed
up the development.
Btw, it would be helpful to give even more details on how the on-chip
IOMMU driver in implemented.
The basic idea is treating MMU (VA->PA) as IOMMU (IOVA->PA). And using
vm_insert_page()/zap_page_range() to do address mapping/unmapping. And
the address mapping will be done in page fault handler because
vm_insert_page() can't be called in atomic_context such
as dma_map_ops->map_page().
Ok, please add it in the cover letter or patch 2 in the next version.
>
> The details and our user case is shown below:
>
> ------------------------
-----------------------------------------------------------
> | APP | | QEMU |
> | --------- | | --------------------
-------------------+<-->+------ |
> | |dev/vdx| | | | device emulation | | virtio
dataplane | | BDS | |
> ------------+-----------
-----------+-----------------------+-----------------+-----
> | | |
|
> | | emulating |
offloading |
>
------------+---------------------------+-----------------------+-----------------+------
> | | block device | | vduse driver | | vdpa
device | | TCP/IP | |
> | -------+-------- --------+--------
+------+------- -----+---- |
> | | | | |
| |
> | | | | |
| |
> | ----------+---------- ----------+----------- | |
| |
> | | virtio-blk driver | | virtio-vdpa driver | | |
| |
> | ----------+---------- ----------+----------- | |
| |
> | | | | |
| |
> | | ------------------ | | |
> | -----------------------------------------------------
---+--- |
>
------------------------------------------------------------------------------
| NIC |---
> ---+---
> |
> ---------+---------
> | Remote Storages |
> -------------------
The figure is not very clear to me in the following points:
1) if the device emulation and virtio dataplane is all implemented in
QEMU, what's the point of doing this? I thought the device should
be a
remove process?
2) it would be better to draw a vDPA bus somewhere to help people to
understand the architecture
3) for the "offloading" I guess it should be done virtio
vhost-vDPA, so
it's better to draw a vhost-vDPA block there
This figure only shows virtio-vdpa case, I will take vhost-vdpa case
into consideration in next version.
Please do that, otherwise this proposal is incomplete.
Thanks
Thanks,
Yongji
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