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Re: [PATCH 3/4] xen: Add DOMAIN_CAPS_DEVICE_MODEL & XEN_DOMCTL_CDF_device_model
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Wed, 11 Jun 2025 00:35:45 -0400
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- Cc: Christian Lindig <christian.lindig@xxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, "Julien Grall" <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 11 Jun 2025 17:14:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-06-11 09:24, Jan Beulich wrote:
On 11.06.2025 00:57, Jason Andryuk wrote:
To add more flexibility in system configuration add the new
DOMAIN_CAPS_DEVICE_MODEL flag and XEN_DOMCTL_CDF_device_model.
Thie new flag corresponds to allowing XSM_DM_PRIV for the domain. This
will enable running device model emulators (QEMU) from the assigne
domain for multiple target domains.
Stubdoms assign target allowing the stubdom to serve as the device
model for a single domain. This new flag allows the single domain to
provide emulators for multiple guests.
The specific scenario is a disaggregated system with the hardware domain
providing device models for muitple guest domains.
Why the hardware domain? Unless a DM also needs access to some of the
physical hardware, it ought to run in a separate domain. Conceivably
such a domain could service multiply guests, so maybe the "single
target" concept presently used for stubdom simply needed extending?
One configuration is the hardware domain running QEMU for the
virtio-gpu. In an earlier iteration, I allowed XSM_DM_PRIV for
is_hardware_domain(). Rightfully, there was some questioning of that
hardcoding. Adding a new flag allows it to be configurable.
Maybe target could be extended. I was thinking that could be left for
the stubdom case as it is today. i.e. a 1-1 device model. But a 1-N
case could be handled this way.
Today dom0 XSM_DM_PRIV falls through to is_control_domain(). The idea
was place a new check directly corresponding to XSM_DM_PRIV.
Regards,
Jason
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