linux-kernel - [PATCH] x86/entry: Fix noinstr warning in __enter_from_user

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Message-Id: <d8955fa6d68dc955dda19baf13ae014ae27926f5.1677369694.git.jpoimboe@kernel.org>
Date:   Sat, 25 Feb 2023 16:01:36 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/entry: Fix noinstr warning in __enter_from_user_mode()

__enter_from_user_mode() is triggering noinstr warnings with
CONFIG_DEBUG_PREEMPT due to its call of preempt_count_add() via
ct_state().

The preemption disable isn't needed as interrupts are already disabled.
And the context_tracking_enabled() check in ct_state() also isn't needed
as that's already being done by the CT_WARN_ON().

Just use __ct_state() instead.

Fixes the following warnings:

  vmlinux.o: warning: objtool: enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section
  vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0xf9: call to preempt_count_add() leaves .noinstr.text section
  vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0xc7: call to preempt_count_add() leaves .noinstr.text section
  vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section

Fixes: 171476775d32 ("context_tracking: Convert state to atomic_t")
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 include/linux/context_tracking.h | 1 +
 kernel/entry/common.c            | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index d4afa8508a80..3a7909ed5498 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -96,6 +96,7 @@ static inline void user_exit_irqoff(void) { }
 static inline int exception_enter(void) { return 0; }
 static inline void exception_exit(enum ctx_state prev_ctx) { }
 static inline int ct_state(void) { return -1; }
+static inline int __ct_state(void) { return -1; }
 static __always_inline bool context_tracking_guest_enter(void) { return false; }
 static inline void context_tracking_guest_exit(void) { }
 #define CT_WARN_ON(cond) do { } while (0)
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 846add8394c4..1314894d2efa 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -21,7 +21,7 @@ static __always_inline void __enter_from_user_mode(struct pt_regs *regs)
 	arch_enter_from_user_mode(regs);
 	lockdep_hardirqs_off(CALLER_ADDR0);
 
-	CT_WARN_ON(ct_state() != CONTEXT_USER);
+	CT_WARN_ON(__ct_state() != CONTEXT_USER);
 	user_exit_irqoff();
 
 	instrumentation_begin();
-- 
2.39.1