x86: Rename variables for debugging

Rename variables for debugging to describe meaning of them precisely.

Also, introduce a generic way to switch IDT by checking a current state,
debug on/off.

Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Link: http://lkml.kernel.org/r/51C323A8.7050905@hds.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>

arch/x86/include/asm/desc.h

@@ -36,8 +36,8 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in
 
 extern struct desc_ptr idt_descr;
 extern gate_desc idt_table[];
-extern struct desc_ptr nmi_idt_descr;
-extern gate_desc nmi_idt_table[];
+extern struct desc_ptr debug_idt_descr;
+extern gate_desc debug_idt_table[];
 
 struct gdt_page {
 	struct desc_struct gdt[GDT_ENTRIES];
@@ -316,7 +316,7 @@ static inline void set_nmi_gate(int gate, void *addr)
 	gate_desc s;
 
 	pack_gate(&s, GATE_INTERRUPT, (unsigned long)addr, 0, 0, __KERNEL_CS);
-	write_idt_entry(nmi_idt_table, gate, &s);
+	write_idt_entry(debug_idt_table, gate, &s);
 }
 #endif
 
@@ -405,4 +405,45 @@ static inline void set_system_intr_gate_ist(int n, void *addr, unsigned ist)
 	_set_gate(n, GATE_INTERRUPT, addr, 0x3, ist, __KERNEL_CS);
 }
 
+#ifdef CONFIG_X86_64
+DECLARE_PER_CPU(u32, debug_idt_ctr);
+static inline bool is_debug_idt_enabled(void)
+{
+	if (this_cpu_read(debug_idt_ctr))
+		return true;
+
+	return false;
+}
+
+static inline void load_debug_idt(void)
+{
+	load_idt((const struct desc_ptr *)&debug_idt_descr);
+}
+#else
+static inline bool is_debug_idt_enabled(void)
+{
+	return false;
+}
+
+static inline void load_debug_idt(void)
+{
+}
+#endif
+
+/*
+ * the load_current_idt() is called with interrupt disabled by local_irq_save()
+ * to avoid races. That way the IDT will always be set back to the expected
+ * descriptor.
+ */
+static inline void load_current_idt(void)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	if (is_debug_idt_enabled())
+		load_debug_idt();
+	else
+		load_idt((const struct desc_ptr *)&idt_descr);
+	local_irq_restore(flags);
+}
 #endif /* _ASM_X86_DESC_H */

arch/x86/kernel/cpu/common.c

@@ -1071,8 +1071,8 @@ __setup("clearcpuid=", setup_disablecpuid);
 
 #ifdef CONFIG_X86_64
 struct desc_ptr idt_descr = { NR_VECTORS * 16 - 1, (unsigned long) idt_table };
-struct desc_ptr nmi_idt_descr = { NR_VECTORS * 16 - 1,
-				    (unsigned long) nmi_idt_table };
+struct desc_ptr debug_idt_descr = { NR_VECTORS * 16 - 1,
+				    (unsigned long) debug_idt_table };
 
 DEFINE_PER_CPU_FIRST(union irq_stack_union,
 		     irq_stack_union) __aligned(PAGE_SIZE);
@@ -1148,20 +1148,20 @@ int is_debug_stack(unsigned long addr)
 		 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
 }
 
-static DEFINE_PER_CPU(u32, debug_stack_use_ctr);
+DEFINE_PER_CPU(u32, debug_idt_ctr);
 
 void debug_stack_set_zero(void)
 {
-	this_cpu_inc(debug_stack_use_ctr);
-	load_idt((const struct desc_ptr *)&nmi_idt_descr);
+	this_cpu_inc(debug_idt_ctr);
+	load_current_idt();
 }
 
 void debug_stack_reset(void)
 {
-	if (WARN_ON(!this_cpu_read(debug_stack_use_ctr)))
+	if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
 		return;
-	if (this_cpu_dec_return(debug_stack_use_ctr) == 0)
-		load_idt((const struct desc_ptr *)&idt_descr);
+	if (this_cpu_dec_return(debug_idt_ctr) == 0)
+		load_current_idt();
 }
 
 #else	/* CONFIG_X86_64 */

arch/x86/kernel/head_64.S

@@ -518,7 +518,7 @@ ENTRY(idt_table)
 	.skip IDT_ENTRIES * 16
 
 	.align L1_CACHE_BYTES
-ENTRY(nmi_idt_table)
+ENTRY(debug_idt_table)
 	.skip IDT_ENTRIES * 16
 
 	__PAGE_ALIGNED_BSS

arch/x86/kernel/traps.c

@@ -785,7 +785,7 @@ void __init trap_init(void)
 	x86_init.irqs.trap_init();
 
 #ifdef CONFIG_X86_64
-	memcpy(&nmi_idt_table, &idt_table, IDT_ENTRIES * 16);
+	memcpy(&debug_idt_table, &idt_table, IDT_ENTRIES * 16);
 	set_nmi_gate(X86_TRAP_DB, &debug);
 	set_nmi_gate(X86_TRAP_BP, &int3);
 #endif