Re: [PATCH qemu.git 0/1] hw/arm/virt: add 2x sp804 timer

[Axel Heider]

Peter,

> > This patch adds timer peripherals to the arm-virt machine.>>
> Is there a reason you can't use the CPU's built-in generic timer
> device ? That is what typical guest code does on this system.
> I'm a bit reluctant to add more devices to the virt board
> because over time it gradually gets increasingly complicated,
> and every new device model we expose to the guest is another
> thing that's part of the security attack surface for guest
> code trying to escape from a KVM VM.

For the seL4 specific case, this is currently not possible in
the standard configuration. It's only exposed for a special
debug and benchmarking configuration.

The catch we have here is, that the virt machine is a nice
generic ARM (and RISC-V) machine for OS testing purposes also,
but it sometimes lacks things (see my other patched for the
UART). So, I wonder what would be the best option to continue
here. Should we consider defining another generic machine
profile that is more suited for the system emulation use case.
This is what OS developer could use then. Or could the virt
machine get some config parameters to customize it further.
So the "Machine-specific options" would  support a "sp804=on"
that would add two timer peripherals then?

The really cool customization option would be passing a DTB
to QEMU that describes exactly what "virt" machine is to be
emulated. I think the Xlinx fork used to support this feature
partly. Not sure if there was ever an attempt to mainline this?
But it would avoid running into a command parameters hell for
customization options.

Axel