I see this topic wasn’t answered yet. Let me give more traction to it since I also have the same
questions since when I started playing with CAmKES VMM.
Please, help/correct me if I’m wrong.
See inline.
From: Jose Martins
Date: Tuesday, 2 November 2021 at 10:12 PM
To: devel@sel4.systems
Subject: [seL4] Camkes VMM configuration
Hello. I've been playing around with the camkes Arm VMM. However, the
meaning of some of the configuration fields is not completely clear to
me. For example:
- what is the difference between "linux_ram_base" and
"linux_ram_paddr_base" in the linux_address_config attribute? Are
these supposed to define the virtual and physical addresses of the
guest's ram region base, respectively? If so, can we have non-identity
mappings by setting them to different values? From my experiments
having different addresses on those does not always work (even if both
are aligned to a 2M superpage boundary) .
JP: Indeed, I think the idea was originally to provide a way to configure VMs
with a 2nd stage mapping that is not 1:1. But I also think this is still work in progress today.
Is it correct?
JP: Looks like linux_ram_base would be the guest-physical baseaddr while
linux_ram_paddr_base the machine-physical.
- what is the difference between the untyped_mmios and mmios
attributes? They seem to serve pretty similar purposes. For example,
in different vm-examples they are both used for assigning the virtual
gic cpu interface to the guest.
JP: I think mmios is used for memory maps with dev attributes,
The mmio of virtual gic cpu interface is one of the mappings where you want
to have dev attributes in the 2nd stage MMU. Untyped_mmios looks like
it is used only for normal memory attributes. For instance, guest ram. Is it correct?
I probably have a few other questions. I couldn't find it, but I was
hoping there was more thorough documentation for the vm configuration
detailing the meaning of these fields (and others)?
JP: I don’t know about documentation, but if the community could give us a pointer,
that would be much appreciated.
Best regards,
José
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