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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@kernel.org>
AuthorDate: Tue, 25 Feb 2020 22:36:46 +01:00
Committer: Thomas Gleixner <tglx@linutronix.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@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Andy Lutomirski <luto@kernel.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);

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