schedule tasks across all cores

Per-core GDT/TSS and AP scheduler entry; fix AP SSE + single_threaded.

test/qemu_test.py

@@ -108,6 +108,11 @@ CASES = [
     {"name": "ipc",
      "expect": r"DANOS-TEST-RESULT: PASS",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
+    # Parallelism: needs more than one core, so this case boots with -smp 4.
+    {"name": "smp",
+     "smp":    4,
+     "expect": r"DANOS-TEST-RESULT: PASS",
+     "fail":   r"DANOS-TEST-RESULT: FAIL"},
     {"name": "fault-ud", "expect": r"invalid opcode \(vector 6\)"},
     {"name": "fault-pf", "expect": r"page fault \(vector 14\)"},
     {"name": "fault-df", "expect": r"double fault \(vector 8\)"},
@@ -175,6 +180,8 @@ def run_case(arch, case):
     fail = re.compile(case["fail"]) if case.get("fail") else None
 
     cmd = [arch["qemu"]] + arch["qemu_args"](arch, esp, vars_fd, serial)
+    if case.get("smp"):  # some cases need more than one core (e.g. parallelism)
+        cmd += ["-smp", str(case["smp"])]
     qemu = subprocess.Popen(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
     try:
         deadline = time.monotonic() + TIMEOUT