[PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init

[Nadav Amit]

There is no apparent reason not to use text_poke_early() while we are
during early-init and we do not patch code that might be on the stack
(i.e., we'll return to the middle of the patched code).  This appears to
be the case of jump-labels, so do so.

This is required for the next patches that would set a temporary mm for
patching, which is initialized after some static-keys are
enabled/disabled.

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
---
 arch/x86/kernel/jump_label.c | 8 +++++++-
 include/linux/kernel.h       | 1 +
 init/main.c                  | 4 ++++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index aac0c1f7e354..367c1d0c20a3 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -52,7 +52,13 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
 	jmp.offset = jump_entry_target(entry) -
 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 
-	if (early_boot_irqs_disabled)
+	/*
+	 * As long as we are in early boot, we can use text_poke_early(), which
+	 * is more efficient: the memory was still not marked as read-only (it
+	 * is only marked after poking_init()). This also prevents us from using
+	 * text_poke() before poking_init() is called.
+	 */
+	if (!early_boot_done)
 		poker = text_poke_early;
 
 	if (type == JUMP_LABEL_JMP) {
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d6aac75b51ba..3e86ff3c64c4 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -564,6 +564,7 @@ extern unsigned long get_taint(void);
 extern int root_mountflags;
 
 extern bool early_boot_irqs_disabled;
+extern u8 early_boot_done;
 
 /*
  * Values used for system_state. Ordering of the states must not be changed
diff --git a/init/main.c b/init/main.c
index a664246450d1..b0fa26637496 100644
--- a/init/main.c
+++ b/init/main.c
@@ -117,6 +117,8 @@ extern void radix_tree_init(void);
  */
 bool early_boot_irqs_disabled __read_mostly;
 
+u8 early_boot_done __read_mostly;
+
 enum system_states system_state __read_mostly;
 EXPORT_SYMBOL(system_state);
 
@@ -735,6 +737,8 @@ asmlinkage __visible void __init start_kernel(void)
 		efi_free_boot_services();
 	}
 
+	early_boot_done = true;
+
 	/* Do the rest non-__init'ed, we're now alive */
 	rest_init();
 }
-- 
2.17.1