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Stage 1: per-VM native stacks, allocated but not yet executed on (FABRIC-3.md §XXVIII)

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Second stage of the preemptive context-switching plan. Every VM (Hera,
every capsule_birth_baby()-born VM including WIREBIND identities) now
gets its own dedicated 2 MiB native C stack at birth -- but nothing runs
on it yet, that's Stage 2. Pure allocation-machinery proof.

Design correction made before writing code: the plan called for cloning
sk_vm_arena_alloc()'s guard-page pattern, but that pattern turns out to
be Mama-only -- host_services.c's kernel_alloc() gives every baby VM a
plain kmalloc() block for its dictionary arena, not a real guarded PMM
allocation. Stacks get the real treatment instead (new
sk_vm_native_stack_alloc()/_free() in arena.c): independent
pmm_alloc_contiguous() + guard pages for every VM without exception, no
singleton, no kmalloc fallback -- a stack overflow is exactly the
failure mode guard pages exist for, and a corrupted stack could corrupt
whatever saved context Stage 2 trusts.

2 MiB size matches this project's own established kernel-stack
convention (g_kernel_stack/g_rpi5_native_stack), not a guess -- that one
shared 2 MiB stack today already carries all VMs' combined nested
VM-EXEC recursion.

Three new VM struct fields, freed in vm_cleanup() alongside the existing
call_stack free. Allocation failure is non-fatal to birth.

All 3 architectures re-verified clean boot to ok>, no native-stack
allocation failures for any Tripod-fleet VM.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016UNhH1mhi52i6Qihh7ZV5S
This commit is contained in:
Robert Allan James
2026-09-13 14:30:46 -04:00
co-authored by Claude Sonnet 5
parent 15672ce17c
commit 57ac3fc304
15 changed files with 27337 additions and 1 deletions
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src/starkernel/vm/vm_core.c
+17
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@@ -364,6 +364,23 @@ void vm_cleanup(VM* vm)
#ifdef __STARKERNEL__
sf_free(vm->call_stack);
vm->call_stack = NULL;
/* FABRIC-3.md §XXVIII, Stage 1 (2026-09-13): free the native stack
* allocated at birth (capsule_birth_baby() / sk_vm_bootstrap_parity()).
* Nothing executes on it yet (that's Stage 2), so there is no
* switched-out-state guard to check here yet -- Stage 2 adds that
* guard at the KILL call sites, before this function is ever reached
* for a VM that would need it. */
if (vm->native_stack_paddr != 0) {
sk_vm_native_stack_t ns;
ns.paddr = vm->native_stack_paddr;
ns.guard_vaddr = vm->native_stack_guard_vaddr;
ns.stack_top = vm->native_stack_top;
sk_vm_native_stack_free(&ns);
vm->native_stack_paddr = 0;
vm->native_stack_guard_vaddr = 0;
vm->native_stack_top = 0;
}
#endif
}