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FABRIC-3.10.8 §7: MC-3 rulings (split 3a/3b/3c; core 0 keeps polling); MC-3a plan

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Robert Allan James
2026-09-26 14:29:22 -04:00
co-authored by Claude Opus 5.5
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@@ -1039,3 +1039,21 @@ The boot hart HSM chose (0) is the one OpenSBI names as `Boot HART ID`.
1. **Stage split.** Proposed: **MC-3a** is the claim and release, `running_on`, the physics lock, the atomic stamps and the per-core decision flag. It changes nothing observable with one worker core, and a probe shows 0 double claims. **MC-3b** is each worker core's interrupt controller and the IPI: core 0 wakes core 1, which counts it and parks again. **MC-3c** is the per-core idle context and wake on work, where workers actually run on core 1. Or all of it as one stage.
2. **Core 0 when idle** (finding §5.2): it polls at about 64% of a host CPU. Proposed: **leave it** in MC-3, since core 0 is the console, USB and timer core and polls by design. Or: core 0 halts until its timer or a device interrupt (a change to the idle point's input path).
**Ruled (Captain Bob, 2026-09-26):** (1) **split into MC-3a / MC-3b / MC-3c** as proposed; (2) **core 0 keeps polling**. MC-3's "idle cores halted" applies to worker cores only.
### 7.5 MC-3a — the claim, the physics lock, per-core decision state (plan)
**Change** (§7.2 items 1, 4, 5 and 6; nothing yet runs on a worker core):
- **`VM.running_on`:** 0 = nobody, else core_id + 1, the same encoding as a lock owner, so a zeroed VM is unclaimed.
- Hera is claimed by core 0 when she becomes current at boot.
- `sk_vm_context_switch()` claims `to` by compare-and-swap. A lost claim returns "not taken" (1), is counted, and its caller re-decides: the trampoline and the idle point go round again, the checkpoint returns.
- `from` is released by whatever next runs on this core (`sk_vm_switch_finish()`): the resumed VM's return from its own switch, or a first-entry trampoline.
- A switch-in that finds its VM claimed by another core counts a **double claim**.
- **Fleet physics lock** `g_lock_physics`, ranked between switch and registry. The public functions of `capsule_vm_physics.c` lock over `*_locked` bodies.
- **Stamps** by atomic fetch-add. **"Decision due"** is per core: a beat sets this core's flag; admitted mail sets every online core's. The switch counter is atomic.
- **`KILL`** refuses a VM whose `running_on` is set, naming the core.
**Evidence (named in advance):**
- **Standard sequence on all three ISAs:** K-10 hashes, G byte-identical (one worker core), all ok `3`, 0 B idle growth, **0 lock-order violations** (so the new rank fits), 0 observer refusals.
- **Probe** (temporary word, amd64): the claim counters after O-A are claims > 0, **lost claims 0, double claims 0**. Posing as core 1, a claim of Hera (held by core 0) **fails** and is counted as lost; with `core_id` back at 0, nothing else changed.