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Xen Summit 2025 - "Virtio Message challenges" design session
- To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Tue, 23 Sep 2025 08:25:19 +0000
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- Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>, "Bill Mills (bill.mills@xxxxxxxxxx)" <bill.mills@xxxxxxxxxx>, "Edgar E. Iglesias" <Edgar.Iglesias@xxxxxxx>
- Delivery-date: Tue, 23 Sep 2025 08:26:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: Xen Summit 2025 - "Virtio Message challenges" design session
Hi,
Here are the notes "Luca Fancellu" took during the design session on Virtio
Message:
-----
Ber: we have challenges in Xen and also other scenarios, I would like to
discuss to don't re-invent the wheel
Main one is that we are introducing "virtually" new VMs (Secure partitions) we
need to define who can be contacted, comprising the secure partition. We have
up to 65k possible peers.
IDs are 32k are for normal world, other 32k for secure.
Initial idea was XSM-Flask, but it goes over its capacity.
We don't want to use xenstored.
Andrew: It's XSM-Flask, what we have was ported from Linux, Xrays can solve, so
we could port it from Linux.
Ber: How do you configure this? At boot time? Can we modify at runtime?
Andrew: You have to reload the policies of the system.
Bertrand: You can have VMs appearing and disappearing, do we think it's the
right solution?
Limitation would be, you will have to have a fixed amount of policies. […]
Anyone has any other idea?
Another problem now, add a discovery system, we don't have xenstored now.
Andrew: The idea is to use argo port zero as an enumeration system.
Bertrand: We need to dig on Argo, and XSM-Flask. Now last problem: VirtIO based
on grant table and event. Main question is should we do this and who is willing
to help?
Who thinks it useful for servers?
Andrew: Legacy SW will be there forever, this thing will help in the long term.
It’s interesting to investigate.
----
Main conclusions:
- Investigate XSM/Flask for defining who is able to communicate with who when
FF-A is used on a system
- Might not be possible/easy to reconfigure at runtime
- Would require the user to define several "profiles" and assign each
VM to a profile
- Example: master can communicate with any VM and secure world, domU
can only communicate with dom0
- Investigate how Argo channel 0 could be used for discovery of Virtio Message
backends
- Define a protocol over Channel 0 to retrieve available
drivers/backend if any
- How do we discover all VMs we can communicate with using Argo ? can
we use XSM ?
- Continue creating a PoC of Virtio Message over Grant-table/xen events
- check performance we can achieve
- check how configuration would work
- check how this can leave on the side of existing pv drivers
If you have any comments or want to add something we missed, please answer to
this mail.
Regards
Bertrand
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