arm64: entry: Add entry and exit functions for debug exceptions

Move the `debug_exception_enter()` and `debug_exception_exit()`
functions from mm/fault.c, as they are needed to split
the debug exceptions entry paths from the current unified one.

Make them externally visible in include/asm/exception.h until
the caller in mm/fault.c is cleaned up.

Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Tested-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Will Deacon <will@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20250707114109.35672-7-ada.coupriediaz@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: Ada Couprie Diaz

arch/arm64/include/asm/exception.h

@@ -80,4 +80,8 @@ void do_serror(struct pt_regs *regs, unsigned long esr);
 void do_signal(struct pt_regs *regs);
 
 void __noreturn panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far);
+
+void debug_exception_enter(struct pt_regs *regs);
+void debug_exception_exit(struct pt_regs *regs);
+
 #endif	/* __ASM_EXCEPTION_H */

arch/arm64/kernel/entry-common.c

@@ -441,6 +441,28 @@ static __always_inline void fpsimd_syscall_exit(void)
 	__this_cpu_write(fpsimd_last_state.to_save, FP_STATE_CURRENT);
 }
 
+/*
+ * In debug exception context, we explicitly disable preemption despite
+ * having interrupts disabled.
+ * This serves two purposes: it makes it much less likely that we would
+ * accidentally schedule in exception context and it will force a warning
+ * if we somehow manage to schedule by accident.
+ */
+void debug_exception_enter(struct pt_regs *regs)
+{
+	preempt_disable();
+
+	/* This code is a bit fragile.  Test it. */
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work");
+}
+NOKPROBE_SYMBOL(debug_exception_enter);
+
+void debug_exception_exit(struct pt_regs *regs)
+{
+	preempt_enable_no_resched();
+}
+NOKPROBE_SYMBOL(debug_exception_exit);
+
 UNHANDLED(el1t, 64, sync)
 UNHANDLED(el1t, 64, irq)
 UNHANDLED(el1t, 64, fiq)

arch/arm64/mm/fault.c

@@ -966,28 +966,6 @@ void __init hook_debug_fault_code(int nr,
 	debug_fault_info[nr].name	= name;
 }
 
-/*
- * In debug exception context, we explicitly disable preemption despite
- * having interrupts disabled.
- * This serves two purposes: it makes it much less likely that we would
- * accidentally schedule in exception context and it will force a warning
- * if we somehow manage to schedule by accident.
- */
-static void debug_exception_enter(struct pt_regs *regs)
-{
-	preempt_disable();
-
-	/* This code is a bit fragile.  Test it. */
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work");
-}
-NOKPROBE_SYMBOL(debug_exception_enter);
-
-static void debug_exception_exit(struct pt_regs *regs)
-{
-	preempt_enable_no_resched();
-}
-NOKPROBE_SYMBOL(debug_exception_exit);
-
 void do_debug_exception(unsigned long addr_if_watchpoint, unsigned long esr,
 			struct pt_regs *regs)
 {