Re: Xen for Apple Silicon (M1 and beyond)

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 25 Jul 2024, Techguru wrote:
> 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.

I just wanted to clarify that I am suggesting to run Xen with 4K pages
and the guests with 16K pages. I am *not* suggesting to change the page
granularity of the guests.