[ADevWithAnIdea]

This PR adds support for the SPTM enabled hypervisor for the base M4 and MacBook Neo on firmware 26.6.2.

The majority of the code, including all of the SPTM emulator, was written by Niklas and carries his signed off by. In areas where I made modifications, his co-authorship is preserved.

It does NOT work on the M4 Max. I have a private branch where it does work, but I do not want to push this due to copyright reasons. See the attached document on the changes required to enable M4 Max (and presumably M4 Pro).

Tested on MacBook Neo.

Changes made to Niklas's patchset:

• refactored some of the page table handling
• dropped the smp patch
• dropped the AMX patch now that the minimal commpage bits were identified
• extended the power guard to m4 max
• some trustcache and amcc fixes required for 26.6.2

M4 Max Bringup Requirements:

Support for my M4 max required four changes to the SPTM emulator, which I will
not contribute for copyright reasons:

## 1. Scale SPTM boot storage with guest memory

The SPTM emulator reserves memory for boot-time objects, metadata describing
each managed memory page, and the page tables needed to map the guest.
Currently, there is a 64 MiB boot arena and bookkeeping for 1024 page tables,
however, larger memory configurations require more metadata and more page
tables. My machine, with 48GB ram, requires roughly 162 MiB of reserved storage
and 1572 page tables.

The fix is to calculate the size of the reservation based on the actual amount
of memory.

## 2. Accommodate additional DART instances

The current emulator has room for 32 DART records. The M4 Max configuration exceeds
that capacity: recorded boots rejected additional DARTs, including identifiers
35 and 36.

Provide enough records for the platform's configured DARTs. The working bringup
environment raises the capacity to 64.

## 3. Preserve unused DART streams locked by firmware

Each DART can have multiple stream identifiers, allowing different device DMA
streams to have separate translation settings. During boot, firmware can lock
these settings so the hypervisor cannot rewrite them.

On the M4 Max, some unused stream slots remain locked with translation enabled
but without a valid root page table. The emulator's policy for those slots
requests a different translation setting. Its existing consistency check treats
that difference as a failure and rejects the DART power-up operation. A recorded
failure occurred on DART 23, stream 15.

Preserve these unused, firmware-locked slots when the requested policy does not
require translation and the hardware has no valid root.

## 4. Separate NVMe hardware tag capacity from queue depth

The NVMe controller uses hardware tags to track outstanding storage commands.
Its memory-management hardware supports 64 tags. The associated count register
uses a zero-based encoding, so the value representing that capacity is 63.

Configure the hardware tag count for its 64-tag capacity independently of the
queue depth. I know there was an issue here with 64 on the base M4, but for the
M4 Max using only 63 breaks.

[niklassheth]

Reading through my code again with more knowledge (and better models), I see a lot of room for improvement. There's a lot of duplicate code like this, I’ll send a PR to clean up the emulator

[niklassheth]

I haven't hit either of these logs, are you hitting this path? If so, this might be neo specific

[ADevWithAnIdea]

very possibly, this is definitely required to boot on my neo-- this device appears particularly cursed, i'll do some A/B testing of the neo vs the m4 max