> That is actually a valid finding. The demo image is not using the GPU
> but this means that we are using GPU RAM for sharing?! Fix for that
> welcome.
>

Regarding the GPU memory, the RPi firmware reserves memory for the GPU from
the top of the first 1G of memory. It's configured by gpu_mem variable in
config.txt and it defaults to 64M. In the default jailhouse-images
configuration, GPU has the range of 0x3b400000-0x40000000 reserved (can be
seen in /proc/device-tree/memreserve), while Jailhouse hypervisor
uses 3fc00000-3fffffff. I don't know if the reserved memory area has any
other use when GPU is not used.

When I connect a FullHD screen to RPi running jailhouse-images, the
framebuffer gets allocated at 0x3e887000-0x3ebfa800, so it doesn't conflict
with any memory region used by Jailhouse. When I used the same
configuration in AGL where the GPU is used with gpu_mem=256M, I was not
able to run the rpi4-linux-demo. But that might have been some other issue,
too, will get back there.

For the AGL setup I want to reserve the memory for Jailhouse (and the
non-root cells) outside of the GPU region using the device tree overlay. I
can port that back into jailhouse/jailhouse-images, if you're interested.

Jakub

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