FABRIC-3.10.8 MC-3b: waking a worker core

Each worker core sets up its own IPI receiver before going online (amd64
LAPIC + vector 0x22 with its own stub, aarch64 banked GIC SGI 0, riscv64
sie.SSIE); core 0 sends by ICR / GICD_SGIR / SBI IPI. Park lets exactly
one interrupt in without a lost-wake window. Boot self-test: IPI round
trips 3/3 and 'woke x3, IPIs x3' on all three ISAs; worker vCPU threads
0.0% on the host. 3-ISA acceptance clean.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/starkernel/arch/amd64/apic.c

@@ -366,6 +366,12 @@ int apic_send_ipi(uint8_t dest_apic_id, uint32_t icr_low)
     return -1; /* still pending: reported by the caller */
 }
 
+void apic_secondary_enable(void)
+{
+    lapic_write(APIC_REG_TPR, 0);
+    lapic_write(APIC_REG_SIVR, 0x100u | APIC_SPURIOUS_VECTOR); /* bit 8: APIC enable */
+}
+
 /* ============================================================================
  * APIC Timer
  * ============================================================================ */

src/starkernel/arch/amd64/interrupts.c

@@ -50,6 +50,7 @@
 #include "apic.h"
 #include "timer.h"
 #include "starkernel/i8042.h"
+#include "starkernel/smp.h" /* FABRIC-3.10.8 MC-3b -- sk_smp_ipi_received() */
 
 /* Set by the FORTH dispatcher just before calling entry->func(vm).
  * Printed on fault to identify which word was executing. */
@@ -346,6 +347,14 @@ void isr_common_handler(uint64_t vector,
         return;
     }
 
+    /* FABRIC-3.10.8 MC-3b: the wake IPI -- counted on the receiving core;
+     * the wake itself is the return from its halt. */
+    if (vector == SK_IPI_VECTOR) {
+        sk_smp_ipi_received();
+        apic_eoi();
+        return;
+    }
+
     /* Handle i8042 keyboard interrupt (item 4.3.5) */
     if (vector == I8042_KEYBOARD_VECTOR) {
         i8042_handle_irq();

src/starkernel/arch/amd64/isr.S

@@ -25,6 +25,7 @@
 .hidden isr_stub0
 .hidden isr_stub32
 .hidden isr_stub33
+.hidden isr_stub34
 .hidden isr_stub_default
 .hidden isr_common_entry
 
@@ -197,7 +198,15 @@ isr_stub33:
     push 33
     jmp isr_common_entry
 
-/* Default stub for other vectors (34-255) */
+/* Stub for the inter-processor wake IPI, vector 0x22 = 34 (FABRIC-3.10.8
+ * MC-3b, SK_IPI_VECTOR) -- its own stub for the reason stub 33 has one. */
+    .global isr_stub34
+isr_stub34:
+    push 0
+    push 34
+    jmp isr_common_entry
+
+/* Default stub for other vectors (35-255) */
 .global isr_stub_default
 isr_stub_default:
     push 0      /* fake error */
@@ -221,7 +230,9 @@ isr_stub_table:
     .quad isr_stub32
     /* Vector 33 = i8042 keyboard IRQ1 (item 4.3.5) */
     .quad isr_stub33
-    /* Vectors 34-255 default to unknown stub */
-    .rept 222
+    /* Vector 34 = the wake IPI (MC-3b) */
+    .quad isr_stub34
+    /* Vectors 35-255 default to unknown stub */
+    .rept 221
         .quad isr_stub_default
     .endr

src/starkernel/arch/amd64/smp.c

@@ -102,9 +102,22 @@ uint32_t arch_smp_enumerate(BootInfo *boot_info, uint64_t *hw_ids, uint32_t cap)
 
 uint64_t arch_smp_boot_hw_id(void) { return apic_id(); }
 
+/* MC-3b: exactly one interrupt may end the halt -- `sti`'s one-instruction
+ * shadow covers the `hlt`, so a wake IPI can't slip in between and be lost. */
 void arch_smp_park_once(void)
 {
-    __asm__ volatile ("cli; hlt" ::: "memory");
+    __asm__ volatile ("sti; hlt; cli" ::: "memory");
+}
+
+void arch_smp_secondary_init(sk_percpu_t *pc)
+{
+    apic_secondary_enable();
+    pc->ipi_target = pc->hw_id; /* the APIC id */
+}
+
+void arch_smp_send_ipi(const sk_percpu_t *target)
+{
+    (void)apic_send_ipi((uint8_t)target->ipi_target, 0x00004000u | SK_IPI_VECTOR); /* fixed, assert */
 }
 
 const char *arch_smp_arrival(const sk_percpu_t *pc)