smp: Force userspace preemption on other cores.

apps/test-loop.c

@@ -0,0 +1,4 @@
+int main(int argc, char * argv[]) {
+	while (1);
+	return 0;
+}

base/usr/include/kernel/arch/x86_64/irq.h

@@ -50,6 +50,7 @@ extern struct regs * _irq12(struct regs*);
 extern struct regs * _irq13(struct regs*);
 extern struct regs * _irq14(struct regs*);
 extern struct regs * _irq15(struct regs*);
+extern struct regs * _isr123(struct regs*);
 extern struct regs * _isr124(struct regs*); /* Does not actually take regs */
 extern struct regs * _isr125(struct regs*); /* Does not actually take regs */
 extern struct regs * _isr126(struct regs*); /* Does not actually take regs */

kernel/arch/x86_64/cmos.c

@@ -233,11 +233,14 @@ void relative_time(unsigned long seconds, unsigned long subseconds, unsigned lon
 	}
 }
 
+void arch_tick_others(void);
+
 int cmos_time_stuff(struct regs *r) {
 	uint64_t timer_ticks, timer_subticks;
 	update_ticks(&timer_ticks, &timer_subticks);
 	wakeup_sleepers(timer_ticks, timer_subticks);
 	irq_ack(0);
+	arch_tick_others();
 	switch_task(1);
 	asm volatile (
 		".global _ret_from_preempt_source\n"

kernel/arch/x86_64/idt.c

@@ -86,6 +86,7 @@ void idt_install(void) {
 	idt_set_gate(46, _irq14, 0x08, 0x8E, 0);
 	idt_set_gate(47, _irq15, 0x08, 0x8E, 0);
 
+	idt_set_gate(123, _isr123, 0x08, 0x8E, 0); /* Clock interrupt for other processors */
 	idt_set_gate(124, _isr124, 0x08, 0x8E, 0); /* Bad TLB shootdown. */
 	idt_set_gate(125, _isr125, 0x08, 0x8E, 0); /* Halts everyone. */
 	idt_set_gate(126, _isr126, 0x08, 0x8E, 0); /* Does nothing, used to exit wait-for-interrupt sleep. */
@@ -234,6 +235,10 @@ struct regs * isr_handler(struct regs * r) {
 			asm volatile("sti");
 			return r;
 		}
+		case 123: {
+			switch_task(1);
+			return r;
+		}
 		case 39: {
 			/* Spurious interrupt */
 			break;

kernel/arch/x86_64/irq.S

@@ -80,6 +80,27 @@ IRQ 15, 47
 /* syscall entry point */
 ISR_NOERR 127
 
+.global _isr123
+.type _isr123, @function
+_isr123:
+    /* Acknowledge IPI */
+    pushq %r12
+    mov (lapic_final), %r12
+    add $0xb0, %r12
+    movl $0, (%r12)
+    popq %r12
+    /* Are we in userspace? */
+    cmpq $8, 8(%rsp)
+    je 1f
+    /* Then we can proceed! */
+    pushq $0x00
+    pushq $123
+    jmp isr_common
+1:
+    /* If we were not in userspace, nothing to do; we were already idle. */
+    iretq
+
+
 .global _isr124
 .type _isr124, @function
 _isr124:

kernel/arch/x86_64/smp.c

@@ -296,6 +296,11 @@ void arch_wakeup_others(void) {
 	lapic_send_ipi(0, 0x7E | (3 << 18));
 }
 
+void arch_tick_others(void) {
+	if (!lapic_final || processor_count < 2) return;
+	lapic_send_ipi(0, 0x7b | (3 << 18));
+}
+
 void arch_tlb_shootdown(uintptr_t vaddr) {
 	if (!lapic_final || processor_count < 2) return;