linux-kernel - [tip: x86/entry] x86/traps: Stop using ist_enter/exit() in do

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Message-ID: <158281400060.28353.1918321204020549760.tip-bot2@tip-bot2>
Date:   Thu, 27 Feb 2020 14:33:20 -0000
From:   "tip-bot2 for Andy Lutomirski" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/entry] x86/traps: Stop using ist_enter/exit() in do_int3()

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     65c668f5faebf549db086b7a6841b6f4187b4e4f
Gitweb:        https://git.kernel.org/tip/65c668f5faebf549db086b7a6841b6f4187b4e4f
Author:        Andy Lutomirski <luto@...nel.org>
AuthorDate:    Tue, 25 Feb 2020 22:36:46 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 27 Feb 2020 15:28:39 +01:00

x86/traps: Stop using ist_enter/exit() in do_int3()

#BP is not longer using IST and using ist_enter() and ist_exit() makes it
harder to change ist_enter() and ist_exit()'s behavior.  Instead open-code
the very small amount of required logic.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Reviewed-by: Andy Lutomirski <luto@...nel.org>
Link: https://lkml.kernel.org/r/20200225220217.150607679@linutronix.de


---
 arch/x86/kernel/traps.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 7ffb6f4..c0bc9df 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -572,14 +572,20 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
 		return;
 
 	/*
-	 * Use ist_enter despite the fact that we don't use an IST stack.
-	 * We can be called from a kprobe in non-CONTEXT_KERNEL kernel
-	 * mode or even during context tracking state changes.
+	 * Unlike any other non-IST entry, we can be called from a kprobe in
+	 * non-CONTEXT_KERNEL kernel mode or even during context tracking
+	 * state changes.  Make sure that we wake up RCU even if we're coming
+	 * from kernel code.
 	 *
-	 * This means that we can't schedule.  That's okay.
+	 * This means that we can't schedule even if we came from a
+	 * preemptible kernel context.  That's okay.
 	 */
-	ist_enter(regs);
+	if (!user_mode(regs)) {
+		rcu_nmi_enter();
+		preempt_disable();
+	}
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
+
 #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
 	if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
 				SIGTRAP) == NOTIFY_STOP)
@@ -600,7 +606,10 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
 	cond_local_irq_disable(regs);
 
 exit:
-	ist_exit(regs);
+	if (!user_mode(regs)) {
+		preempt_enable_no_resched();
+		rcu_nmi_exit();
+	}
 }
 NOKPROBE_SYMBOL(do_int3);