[arch][x86][lapic] a little bit of restructuring of some recent lapic code

Functionally equivalent, but refactor two copies of local apic
initialization code into a shared routine.

arch/x86/32/start.S

@@ -178,6 +178,7 @@ main_lk:
     call setup_idt
 
     /* set up the percpu data structure pointer for the boot cpu */
+    /* NOTE: assumes the local apic is 0, which is probably not a safe assumption. */
     pushl $0
     pushl $0
     call x86_configure_percpu_early

arch/x86/64/start.S

@@ -216,6 +216,7 @@ highaddr:
     call setup_idt
 
     /* set up the percpu data structure pointer for the boot cpu */
+    /* NOTE: assumes the local apic is 0, which is probably not a safe assumption. */
     xor %edi, %edi
     xor %esi, %esi
     call x86_configure_percpu_early

arch/x86/include/arch/x86/lapic.h

@@ -15,13 +15,18 @@
 
 // local apic
 void lapic_init(void);
-uint32_t lapic_get_id_from_hardware(void);
 status_t lapic_timer_init(bool invariant_tsc_supported);
 void lapic_eoi(unsigned int vector);
 void lapic_send_init_ipi(uint32_t apic_id, bool level);
 void lapic_send_startup_ipi(uint32_t apic_id, uint32_t startup_vector);
 void lapic_send_ipi(uint32_t apic_id, mp_ipi_t ipi);
 
+// enable the local apic on the current cpu, panic if not present
+void lapic_enable_on_local_cpu(void);
+
+// read the apic id of the local apic on the current cpu, assumes lapic is present
+uint32_t lapic_get_apic_id(void);
+
 status_t lapic_set_oneshot_timer(platform_timer_callback callback, void *arg, lk_time_t interval);
 void lapic_cancel_timer(void);
 

arch/x86/lapic.c

@@ -267,13 +267,10 @@ static void lapic_init_postvm(uint level) {
 LK_INIT_HOOK(lapic_init_postvm, lapic_init_postvm, LK_INIT_LEVEL_VM + 1);
 
 static void lapic_init_percpu(uint level) {
-    // Make sure the apic is enabled and x2apic mode is set (if supported)
+    // If we're on a secondary cpu we should have a local apic detected and present
-    uint64_t apic_base = read_msr(X86_MSR_IA32_APIC_BASE);
+    DEBUG_ASSERT(lapic_present);
-    apic_base |= (1u<<11);
+
-    if (lapic_x2apic) {
+    lapic_enable_on_local_cpu();
-        apic_base |= (1u<<10);
-    }
-    write_msr(X86_MSR_IA32_APIC_BASE, apic_base);
 
     // set the spurious vector register
     uint32_t svr = (LAPIC_INT_SPURIOUS | (1u<<8)); // enable
@@ -287,9 +284,21 @@ static void lapic_init_percpu(uint level) {
 }
 LK_INIT_HOOK_FLAGS(lapic_init_percpu, lapic_init_percpu, LK_INIT_LEVEL_VM, LK_INIT_FLAG_SECONDARY_CPUS);
 
-uint32_t lapic_get_id_from_hardware(void) {
+void lapic_enable_on_local_cpu(void) {
+    DEBUG_ASSERT(lapic_present);
+
+    // Make sure the apic is enabled and x2apic mode is set (if supported)
+    uint64_t apic_base = read_msr(X86_MSR_IA32_APIC_BASE);
+    apic_base |= (1u<<11);
+    if (lapic_x2apic) {
+        apic_base |= (1u<<10);
+    }
+    write_msr(X86_MSR_IA32_APIC_BASE, apic_base);
+}
+
+uint32_t lapic_get_apic_id(void) {
     if (!lapic_present) {
-        return 0;
+        return -1;
     }
 
     if (lapic_x2apic) {

arch/x86/mp.c

@@ -87,35 +87,13 @@ status_t arch_mp_send_ipi(mp_cpu_mask_t target, mp_ipi_t ipi) {
 
 void arch_mp_init_percpu(void) {}
 
-/* 
-*  Move to lapic.c
-*
-uint32_t x86_get_apic_id_from_hardware(void) {
-    uint32_t unused = 0, ecx = 0;
-    cpuid(0x1, &unused, &unused, &ecx, &unused);
-
-    if (ecx & (1u << 21)) {
-        // read full 32bit apic id from x2apic msr if available
-        return (uint32_t)read_msr(0x802);
-    } else {
-        // read the apic id out of cpuid leaf 1, which should be present if SMP is enabled.
-        uint32_t apic_id;
-        cpuid(0x1, &unused, &apic_id, &unused, &unused);
-
-        apic_id >>= 24;
-        return apic_id;
-    }
-}
-*/
-
 void x86_secondary_entry(uint cpu_num) {
-    if (x86_feature_test(X86_FEATURE_X2APIC)) {
+    // Read the local apic id from the local apic.
-        uint64_t apic_base = read_msr(X86_MSR_IA32_APIC_BASE);
+    // NOTE: assumes a local apic is present but since this is a secondary cpu,
-        apic_base |= (1u << 10);
+    // it should be a safe assumption.
-        write_msr(X86_MSR_IA32_APIC_BASE, apic_base);
+    lapic_enable_on_local_cpu();
-    }
+    uint32_t apic_id = lapic_get_apic_id();
 
-    uint32_t apic_id = lapic_get_id_from_hardware();
     x86_configure_percpu_early(cpu_num, apic_id);
 
     x86_early_init_percpu();