Re: Xen for Apple Silicon (M1 and beyond)

[Techguru <techguru@xxxxxxxx>]

A bit about Apple Silicon M1(2,3,4) architecture, SoC and motherboard. (AFAIK)

There are no EFI assumptions nor contracts, and no EFI firmware.

Between those 4 generations of silicon, there are about 80 different roles "SoC cores/components" can play, each with its own signed Apple Firmware.

Most of those SoC cores/functions have nothing to do with the traditional ARM compute cores.

At least one of those SoC cores is actually an x86 processor core (on models which support HDMI), running x86 firmware.

Many of the other non-compute cores (Networking, USC (A-C), Thunderbolt ... yada yada) are various size Arm cores running an Apple RTOS Variant of L4 microkernel.

Each of those, again, has its own Apple Signed firmware which is paired with a particular Darwin kernel release.

One point of friction is that there is no stable ABI spec for each of the firmware modules.   Apple reserves the right to completely change the firmware's

interface with the paired Darwin kernel.

It is perhaps best to think of the SoC and related motherboard hardware as a "compute cluster" rather than a single von-neuman machine.

I could be wrong about a lot of the above, and invite corrections with citations.

For this, do you know if 4K pages are supported (in addition to 16K)? It
would be a lot easier to keep running Xen using 4K pages and run guests
on top of Xen which use 16K pages. In the past, we had Linux using 64K
pages running on top of Xen using 4K pages for example.

Given the state of all of the _other_ SoC cores running L4 RTOS, I have reservations about running with anything other than 16k native pages.  Will have to

investigate what options, if any, are available for keeping 16k pages for existing firmware, while presenting 4k pages to guest OS.

However, both Rosetta and Docker appear to run 4k guests just fine, so not sure how many pushups they are doing in the process.

TBD

  device trees;
 
You might be able to use the device tree which is used to boot Linux on
Apple silicon

Yes, the Asahi team has done some wizard level heavy lifting in that area.  If I recall correctly, their model is let apple boot loader load the apple signed firmware, pass off to the Asahi boot kernel,  then present an EFI compatible DT and driver surface on top of that for boot-essential drivers.  They also have a fairly nifty lightweight hypervisor that assists with debug and ultimately does boot via u-boot -> grub -> linux in the current incarnation