x86/entry: Move irq tracing on syscall entry to C-code

Now that the C entry points are safe, move the irq flags tracing code into
the entry helper:

    - Invoke lockdep before calling into context tracking

    - Use the safe trace_hardirqs_on_prepare() trace function after context
      tracking established state and RCU is watching.

enter_from_user_mode() is also still invoked from the exception/interrupt
entry code which still contains the ASM irq flags tracing. So this is just
a redundant and harmless invocation of tracing / lockdep until these are
removed as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134340.611961721@linutronix.de

arch/x86/entry/common.c

@@ -40,19 +40,36 @@
 #include <trace/events/syscalls.h>
 
 #ifdef CONFIG_CONTEXT_TRACKING
-/* Called on entry from user mode with IRQs off. */
+/**
+ * enter_from_user_mode - Establish state when coming from user mode
+ *
+ * Syscall entry disables interrupts, but user mode is traced as interrupts
+ * enabled. Also with NO_HZ_FULL RCU might be idle.
+ *
+ * 1) Tell lockdep that interrupts are disabled
+ * 2) Invoke context tracking if enabled to reactivate RCU
+ * 3) Trace interrupts off state
+ */
 __visible noinstr void enter_from_user_mode(void)
 {
 	enum ctx_state state = ct_state();
 
+	lockdep_hardirqs_off(CALLER_ADDR0);
 	user_exit_irqoff();
 
 	instrumentation_begin();
 	CT_WARN_ON(state != CONTEXT_USER);
+	trace_hardirqs_off_prepare();
 	instrumentation_end();
 }
 #else
-static inline void enter_from_user_mode(void) {}
+static __always_inline void enter_from_user_mode(void)
+{
+	lockdep_hardirqs_off(CALLER_ADDR0);
+	instrumentation_begin();
+	trace_hardirqs_off_prepare();
+	instrumentation_end();
+}
 #endif
 
 static noinstr void exit_to_user_mode(void)

arch/x86/entry/entry_32.S

@@ -967,12 +967,6 @@ SYM_FUNC_START(entry_SYSENTER_32)
 	jnz	.Lsysenter_fix_flags
 .Lsysenter_flags_fixed:
 
-	/*
-	 * User mode is traced as though IRQs are on, and SYSENTER
-	 * turned them off.
-	 */
-	TRACE_IRQS_OFF
-
 	movl	%esp, %eax
 	call	do_fast_syscall_32
 	/* XEN PV guests always use IRET path */
@@ -1082,12 +1076,6 @@ SYM_FUNC_START(entry_INT80_32)
 
 	SAVE_ALL pt_regs_ax=$-ENOSYS switch_stacks=1	/* save rest */
 
-	/*
-	 * User mode is traced as though IRQs are on, and the interrupt gate
-	 * turned them off.
-	 */
-	TRACE_IRQS_OFF
-
 	movl	%esp, %eax
 	call	do_int80_syscall_32
 .Lsyscall_32_done:

arch/x86/entry/entry_64.S

@@ -167,8 +167,6 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
 
 	PUSH_AND_CLEAR_REGS rax=$-ENOSYS
 
-	TRACE_IRQS_OFF
-
 	/* IRQs are off. */
 	movq	%rax, %rdi
 	movq	%rsp, %rsi

arch/x86/entry/entry_64_compat.S

@@ -129,12 +129,6 @@ SYM_FUNC_START(entry_SYSENTER_compat)
 	jnz	.Lsysenter_fix_flags
 .Lsysenter_flags_fixed:
 
-	/*
-	 * User mode is traced as though IRQs are on, and SYSENTER
-	 * turned them off.
-	 */
-	TRACE_IRQS_OFF
-
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
 	/* XEN PV guests always use IRET path */
@@ -247,12 +241,6 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
 	pushq   $0			/* pt_regs->r15 = 0 */
 	xorl	%r15d, %r15d		/* nospec   r15 */
 
-	/*
-	 * User mode is traced as though IRQs are on, and SYSENTER
-	 * turned them off.
-	 */
-	TRACE_IRQS_OFF
-
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
 	/* XEN PV guests always use IRET path */
@@ -403,12 +391,6 @@ SYM_CODE_START(entry_INT80_compat)
 	xorl	%r15d, %r15d		/* nospec   r15 */
 	cld
 
-	/*
-	 * User mode is traced as though IRQs are on, and the interrupt
-	 * gate turned them off.
-	 */
-	TRACE_IRQS_OFF
-
 	movq	%rsp, %rdi
 	call	do_int80_syscall_32
 .Lsyscall_32_done: