x86/entry: Convert Debug exception to IDTENTRY_DB

Convert #DB to IDTENTRY_ERRORCODE:
  - Implement the C entry point with DEFINE_IDTENTRY_DB
  - Emit the ASM stub with DECLARE_IDTENTRY
  - Remove the ASM idtentry in 64bit
  - Remove the open coded ASM entry code in 32bit
  - Fixup the XEN/PV code
  - Remove the old prototypes

No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505135314.900297476@linutronix.de

arch/x86/entry/entry_32.S

@@ -1488,16 +1488,6 @@ ret_to_user:
 	jmp	restore_all_switch_stack
 SYM_CODE_END(handle_exception)
 
-SYM_CODE_START(debug)
-	/*
-	 * Entry from sysenter is now handled in common_exception
-	 */
-	ASM_CLAC
-	pushl	$0
-	pushl	$do_debug
-	jmp	common_exception
-SYM_CODE_END(debug)
-
 SYM_CODE_START(double_fault)
 1:
 	/*

arch/x86/entry/entry_64.S

@@ -1074,12 +1074,10 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
 
 idtentry	X86_TRAP_PF		page_fault		do_page_fault			has_error_code=1
 
-idtentry_mce_db	X86_TRAP_DB		debug			do_debug
 idtentry_df	X86_TRAP_DF		double_fault		do_double_fault
 
 #ifdef CONFIG_XEN_PV
 idtentry	512 /* dummy */		hypervisor_callback	xen_do_hypervisor_callback	has_error_code=0
-idtentry	X86_TRAP_DB		xendebug		do_debug			has_error_code=0
 #endif
 
 /*

arch/x86/include/asm/idtentry.h

@@ -262,4 +262,8 @@ DECLARE_IDTENTRY_MCE(X86_TRAP_MC,	exc_machine_check);
 DECLARE_IDTENTRY_NMI(X86_TRAP_NMI,	exc_nmi);
 DECLARE_IDTENTRY_XEN(X86_TRAP_NMI,	nmi);
 
+/* #DB */
+DECLARE_IDTENTRY_DEBUG(X86_TRAP_DB,	exc_debug);
+DECLARE_IDTENTRY_XEN(X86_TRAP_DB,	debug);
+
 #endif

arch/x86/include/asm/traps.h

@@ -11,7 +11,6 @@
 
 #define dotraplinkage __visible
 
-asmlinkage void debug(void);
 #ifdef CONFIG_X86_64
 asmlinkage void double_fault(void);
 #endif
@@ -19,12 +18,10 @@ asmlinkage void page_fault(void);
 asmlinkage void async_page_fault(void);
 
 #if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
-asmlinkage void xen_xendebug(void);
 asmlinkage void xen_double_fault(void);
 asmlinkage void xen_page_fault(void);
 #endif
 
-dotraplinkage void do_debug(struct pt_regs *regs, long error_code);
 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2);
 dotraplinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address);
 

arch/x86/kernel/idt.c

@@ -59,7 +59,7 @@ static bool idt_setup_done __initdata;
  * stacks work only after cpu_init().
  */
 static const __initconst struct idt_data early_idts[] = {
-	INTG(X86_TRAP_DB,		debug),
+	INTG(X86_TRAP_DB,		asm_exc_debug),
 	SYSG(X86_TRAP_BP,		asm_exc_int3),
 #ifdef CONFIG_X86_32
 	INTG(X86_TRAP_PF,		page_fault),
@@ -93,7 +93,7 @@ static const __initconst struct idt_data def_idts[] = {
 #else
 	INTG(X86_TRAP_DF,		double_fault),
 #endif
-	INTG(X86_TRAP_DB,		debug),
+	INTG(X86_TRAP_DB,		asm_exc_debug),
 
 #ifdef CONFIG_X86_MCE
 	INTG(X86_TRAP_MC,		asm_exc_machine_check),
@@ -164,7 +164,7 @@ static const __initconst struct idt_data early_pf_idts[] = {
  * stack set to DEFAULT_STACK (0). Required for NMI trap handling.
  */
 static const __initconst struct idt_data dbg_idts[] = {
-	INTG(X86_TRAP_DB,	debug),
+	INTG(X86_TRAP_DB,		asm_exc_debug),
 };
 #endif
 
@@ -185,7 +185,7 @@ gate_desc debug_idt_table[IDT_ENTRIES] __page_aligned_bss;
  * cpu_init() when the TSS has been initialized.
  */
 static const __initconst struct idt_data ist_idts[] = {
-	ISTG(X86_TRAP_DB,	debug,			IST_INDEX_DB),
+	ISTG(X86_TRAP_DB,	asm_exc_debug,		IST_INDEX_DB),
 	ISTG(X86_TRAP_NMI,	asm_exc_nmi,		IST_INDEX_NMI),
 	ISTG(X86_TRAP_DF,	double_fault,		IST_INDEX_DF),
 #ifdef CONFIG_X86_MCE

arch/x86/kernel/traps.c

@@ -775,7 +775,7 @@ static __always_inline void debug_exit(unsigned long dr7)
  *
  * May run on IST stack.
  */
-dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
+DEFINE_IDTENTRY_DEBUG(exc_debug)
 {
 	struct task_struct *tsk = current;
 	unsigned long dr6, dr7;
@@ -784,6 +784,9 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 
 	debug_enter(&dr6, &dr7);
 
+	if (user_mode(regs))
+		idtentry_enter(regs);
+	else
 		nmi_enter();
 
 	/*
@@ -821,7 +824,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 		goto exit;
 #endif
 
-	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
+	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,
 		       SIGTRAP) == NOTIFY_STOP)
 		goto exit;
 
@@ -835,7 +838,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 	cond_local_irq_enable(regs);
 
 	if (v8086_mode(regs)) {
-		handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code,
+		handle_vm86_trap((struct kernel_vm86_regs *) regs, 0,
 				 X86_TRAP_DB);
 		cond_local_irq_disable(regs);
 		debug_stack_usage_dec();
@@ -855,15 +858,17 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 	}
 	si_code = get_si_code(tsk->thread.debugreg6);
 	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
-		send_sigtrap(regs, error_code, si_code);
+		send_sigtrap(regs, 0, si_code);
 	cond_local_irq_disable(regs);
 	debug_stack_usage_dec();
 
 exit:
+	if (user_mode(regs))
+		idtentry_exit(regs);
+	else
 		nmi_exit();
 	debug_exit(dr7);
 }
-NOKPROBE_SYMBOL(do_debug);
 
 /*
  * Note that we play around with the 'TS' bit in an attempt to get

arch/x86/xen/enlighten_pv.c

@@ -615,7 +615,7 @@ struct trap_array_entry {
 	.ist_okay	= ist_ok }
 
 static struct trap_array_entry trap_array[] = {
-	{ debug,                       xen_xendebug,                    true },
+	TRAP_ENTRY_REDIR(exc_debug, exc_xendebug,	true  ),
 	{ double_fault,                xen_double_fault,                true },
 #ifdef CONFIG_X86_MCE
 	TRAP_ENTRY(exc_machine_check,			true  ),

arch/x86/xen/xen-asm_64.S

@@ -29,8 +29,8 @@ _ASM_NOKPROBE(xen_\name)
 .endm
 
 xen_pv_trap asm_exc_divide_error
-xen_pv_trap debug
-xen_pv_trap xendebug
+xen_pv_trap asm_exc_debug
+xen_pv_trap asm_exc_xendebug
 xen_pv_trap asm_exc_int3
 xen_pv_trap asm_exc_xennmi
 xen_pv_trap asm_exc_overflow