arm64: entry: move enter_from_user_mode to entry-common.c

In later patches we'll want to extend enter_from_user_mode() and add a
corresponding exit_to_user_mode(). As these will be common for all
entries/exits from userspace, it'd be better for these to live in
entry-common.c with the rest of the entry logic.

This patch moves enter_from_user_mode() into entry-common.c. As with
other functions in entry-common.c it is marked as noinstr (which
prevents all instrumentation, tracing, and kprobes) but there are no
other functional changes.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201130115950.22492-5-mark.rutland@arm.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/entry-common.c

@@ -101,6 +101,12 @@ asmlinkage void noinstr el1_sync_handler(struct pt_regs *regs)
 	}
 }
 
+asmlinkage void noinstr enter_from_user_mode(void)
+{
+	CT_WARN_ON(ct_state() != CONTEXT_USER);
+	user_exit_irqoff();
+}
+
 static void noinstr el0_da(struct pt_regs *regs, unsigned long esr)
 {
 	unsigned long far = read_sysreg(far_el1);

arch/arm64/kernel/traps.c

@@ -876,13 +876,6 @@ asmlinkage void do_serror(struct pt_regs *regs, unsigned int esr)
 	nmi_exit();
 }
 
-asmlinkage void enter_from_user_mode(void)
-{
-	CT_WARN_ON(ct_state() != CONTEXT_USER);
-	user_exit_irqoff();
-}
-NOKPROBE_SYMBOL(enter_from_user_mode);
-
 /* GENERIC_BUG traps */
 
 int is_valid_bugaddr(unsigned long addr)