On 18 Apr 2024, at 08:02, Isaac Beckett <isaactbeck...@gmail.com> wrote:

Sorry, I should clarify. I meant making a dynamic OS that uses the sDDF. Not on 
Microkit, since it’s not meant for that. But something that is more flexible at 
runtime, designed for general purpose use so that it can load components when 
they’re needed instead of having a fixed set of components running at all times.

The sDDF is not inherently dependent on the Microkit. It uses Notifications and 
memory regions as abstracted by the Microkit, and is structured as Microkit 
event handlers.

It should be straightforward to provide wrappers of this functionality from 
other OSes. I actually planned on getting this done, but it was somehow 
dropped. We do want the sDDF to be usable by other seL4-based OSes.

While I was thinking of that I also got another idea. Some graphics cards 
support technology similar to hardware virtualization extensions on CPUs, such 
that they can be configured (with appropriate drivers, of course) to behave as 
multiple logical devices on one physical device. The term for this I believe is 
SR-IOV.

Similar features are provided by “self-virtualising” NICs (see comment in 
S5.1.2 of the sDDF Design doc). Yes, to make use of this you’d need a small 
driver to set up the virtual devices, and then each one would appear as a 
separate device with its own driver (incl mapping some of them as pass-through 
devices to Linux). And yes, you’d get timing channels as with any shared 
hardware resources.

Gernot
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