x86/irq: Get rid of the 'first_system_vector' indirection bogosity

This variable is beyond pointless. Nothing allocates a vector via
alloc_gate() below FIRST_SYSTEM_VECTOR. So nothing can change
first_system_vector.

If there is a need for a gate below FIRST_SYSTEM_VECTOR then it can be
added to the vector defines and FIRST_SYSTEM_VECTOR can be adjusted
accordingly.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064956.357109735@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/desc.h

@@ -5,6 +5,7 @@
 #include <asm/ldt.h>
 #include <asm/mmu.h>
 #include <asm/fixmap.h>
+#include <asm/irq_vectors.h>
 
 #include <linux/smp.h>
 #include <linux/percpu.h>
@@ -482,16 +483,14 @@ static inline void _set_gate(int gate, unsigned type, void *addr,
 				0, 0, __KERNEL_CS);			\
 	} while (0)
 
-extern int first_system_vector;
 /* used_vectors is BITMAP for irq is not managed by percpu vector_irq */
 extern unsigned long used_vectors[];
 
 static inline void alloc_system_vector(int vector)
 {
+	BUG_ON(vector < FIRST_SYSTEM_VECTOR);
 	if (!test_bit(vector, used_vectors)) {
 		set_bit(vector, used_vectors);
-		if (first_system_vector > vector)
-			first_system_vector = vector;
 	} else {
 		BUG();
 	}

arch/x86/kernel/apic/apic.c

@@ -177,8 +177,6 @@ static int disable_apic_timer __initdata;
 int local_apic_timer_c2_ok;
 EXPORT_SYMBOL_GPL(local_apic_timer_c2_ok);
 
-int first_system_vector = FIRST_SYSTEM_VECTOR;
-
 /*
  * Debug level, exported for io_apic.c
  */

arch/x86/kernel/apic/vector.c

@@ -166,7 +166,7 @@ static int __assign_irq_vector(int irq, struct apic_chip_data *d,
 		offset = current_offset;
 next:
 		vector += 16;
-		if (vector >= first_system_vector) {
+		if (vector >= FIRST_SYSTEM_VECTOR) {
 			offset = (offset + 1) % 16;
 			vector = FIRST_EXTERNAL_VECTOR + offset;
 		}

arch/x86/kernel/irq.c

@@ -429,7 +429,7 @@ int check_irq_vectors_for_cpu_disable(void)
 		 * this w/o holding vector_lock.
 		 */
 		for (vector = FIRST_EXTERNAL_VECTOR;
-		     vector < first_system_vector; vector++) {
+		     vector < FIRST_SYSTEM_VECTOR; vector++) {
 			if (!test_bit(vector, used_vectors) &&
 			    IS_ERR_OR_NULL(per_cpu(vector_irq, cpu)[vector])) {
 				if (++count == this_count)

arch/x86/kernel/irqinit.c

@@ -169,10 +169,7 @@ void __init native_init_IRQ(void)
 	 * 'special' SMP interrupts)
 	 */
 	i = FIRST_EXTERNAL_VECTOR;
-#ifndef CONFIG_X86_LOCAL_APIC
-#define first_system_vector NR_VECTORS
-#endif
-	for_each_clear_bit_from(i, used_vectors, first_system_vector) {
+	for_each_clear_bit_from(i, used_vectors, FIRST_SYSTEM_VECTOR) {
 		/* IA32_SYSCALL_VECTOR could be used in trap_init already. */
 		set_intr_gate(i, irq_entries_start +
 				8 * (i - FIRST_EXTERNAL_VECTOR));