x86/idt: Consolidate IDT invalidation

kexec and reboot have both code to invalidate IDT. Create a common function
and use it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
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/20170828064958.600953282@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/desc.h

@@ -503,4 +503,7 @@ static inline void load_current_idt(void)
 	else
 		load_idt((const struct desc_ptr *)&idt_descr);
 }
+
+extern void idt_invalidate(void *addr);
+
 #endif /* _ASM_X86_DESC_H */

arch/x86/kernel/idt.c

@@ -24,3 +24,14 @@ const struct desc_ptr debug_idt_descr = {
 	.address	= (unsigned long) debug_idt_table,
 };
 #endif
+
+/**
+ * idt_invalidate - Invalidate interrupt descriptor table
+ * @addr:	The virtual address of the 'invalid' IDT
+ */
+void idt_invalidate(void *addr)
+{
+	struct desc_ptr idt = { .address = (unsigned long) addr, .size = 0 };
+
+	load_idt(&idt);
+}

arch/x86/kernel/machine_kexec_32.c

@@ -26,18 +26,6 @@
 #include <asm/set_memory.h>
 #include <asm/debugreg.h>
 
-static void set_idt(void *newidt, __u16 limit)
-{
-	struct desc_ptr curidt;
-
-	/* ia32 supports unaliged loads & stores */
-	curidt.size    = limit;
-	curidt.address = (unsigned long)newidt;
-
-	load_idt(&curidt);
-}
-
-
 static void set_gdt(void *newgdt, __u16 limit)
 {
 	struct desc_ptr curgdt;
@@ -245,7 +233,7 @@ void machine_kexec(struct kimage *image)
 	 * If you want to load them you must set up your own idt & gdt.
 	 */
 	set_gdt(phys_to_virt(0), 0);
-	set_idt(phys_to_virt(0), 0);
+	idt_invalidate(phys_to_virt(0));
 
 	/* now call it */
 	image->start = relocate_kernel_ptr((unsigned long)image->head,

arch/x86/kernel/reboot.c

@@ -38,8 +38,6 @@
 void (*pm_power_off)(void);
 EXPORT_SYMBOL(pm_power_off);
 
-static const struct desc_ptr no_idt = {};
-
 /*
  * This is set if we need to go through the 'emergency' path.
  * When machine_emergency_restart() is called, we may be on
@@ -638,7 +636,7 @@ static void native_machine_emergency_restart(void)
 			break;
 
 		case BOOT_TRIPLE:
-			load_idt(&no_idt);
+			idt_invalidate(NULL);
 			__asm__ __volatile__("int3");
 
 			/* We're probably dead after this, but... */