[RFC PATCH 08/14] BROKEN: context_tracking: Make context_tracking_key __ro_after_init

objtool now warns about it:

  vmlinux.o: warning: objtool: enter_from_user_mode+0x4e: Non __ro_after_init static key "context_tracking_key" in .noinstr section
  vmlinux.o: warning: objtool: enter_from_user_mode+0x50: Non __ro_after_init static key "context_tracking_key" in .noinstr section
  vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x60: Non __ro_after_init static key "context_tracking_key" in .noinstr section
  vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x62: Non __ro_after_init static key "context_tracking_key" in .noinstr section
  [...]

The key can only be enabled (and not disabled) in the __init function
ct_cpu_tracker_user(), so mark it as __ro_after_init.

BROKEN: the struct static_key lives in a read-only mapping after
mark_rodata_ro(), which falls apart when the KVM module is loaded after
init and a write to the struct happens due to e.g. guest_state_exit_irqoff()
relying on the static key:

  jump_label_add_module()
  `\
    static_key_set_mod()
    static_key_set_linked()

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 kernel/context_tracking.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index a09f1c19336ae..4e6cb14272fcb 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c

@@ -432,7 +432,7 @@ static __always_inline void ct_kernel_enter(bool user, int offset) { }
 #define CREATE_TRACE_POINTS
 #include <trace/events/context_tracking.h>
 
-DEFINE_STATIC_KEY_FALSE(context_tracking_key);
+DEFINE_STATIC_KEY_FALSE_RO(context_tracking_key);
 EXPORT_SYMBOL_GPL(context_tracking_key);
 
 static noinstr bool context_tracking_recursion_enter(void)

-- 
2.31.1