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Re: question about virtio-vsock on xen
- To: Peng Fan <peng.fan@xxxxxxx>
- From: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>
- Date: Mon, 26 Feb 2024 20:16:16 +0000
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- Cc: Julien Grall <julien@xxxxxxx>, "vikram.garhwal@xxxxxxx" <vikram.garhwal@xxxxxxx>, Leo Yan <leo.yan@xxxxxxxxxx>, Viresh Kumar <viresh.kumar@xxxxxxxxxx>, Stewart Hildebrand <stewart.hildebrand@xxxxxxx>, "sgarzare@xxxxxxxxxx" <sgarzare@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxx>
- Delivery-date: Mon, 26 Feb 2024 20:16:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AdpmUSXKZvg8Aft6RRu9smUwoggtbwAUAHAAACuPlYAARFRfYAAj+0EA
- Thread-topic: question about virtio-vsock on xen
On 26.02.24 05:09, Peng Fan wrote:
> Hi Oleksandr,
Hello Peng
[snip]
>>
>> ... Peng, we have vhost-vsock (and vhost-net) Xen PoC. Although it is
>> non-
>> upstreamable in its current shape (based on old Linux version, requires some
>> rework and proper integration, most likely requires involving Qemu and
>> protocol changes to pass an additional info to vhost), it works with Linux
>> v5.10 + patched Qemu v7.0, so you can refer to the Yocto meta layer which
>> contains kernel patches for the details [1].
>
> Thanks for the pointer, I am reading the code.
>
>>
>> In a nutshell, before accessing the guest data the host module needs to map
>> descriptors in virtio rings which contain either guest grant based DMA
>> addresses (by using Xen grant mappings) or guest pseudo-physical addresses
>> (by using Xen foreign mappings). After accessing the guest data the host
>> module needs to unmap them.
>
> Ok, I thought the current xen virtio code already map every ready.
>
It does, as you said the virtio-blk-pci worked in your environment. But
vhost(-vsock) is a special case, unlike for virtio-blk-pci where the
whole backend resides in Qemu, here we have a split model. As I
understand the Qemu performs only initial setup/configuration then
offloads the I/O processing to a separate entity which is the Linux
module in that particular case.
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