linux-kernel - [RFC][PATCH 7/7] x86/debug: Move cond_local_irq_enable() block into exc_debug

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Message-ID: <20200820104905.470593910@infradead.org>
Date:   Thu, 20 Aug 2020 12:38:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Kyle Huey <me@...ehuey.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Robert O'Callahan <rocallahan@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [RFC][PATCH 7/7] x86/debug: Move cond_local_irq_enable() block into exc_debug_user()


Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/traps.c |   65 +++++++++++++++++++++++-------------------------
 1 file changed, 32 insertions(+), 33 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -783,41 +783,15 @@ static __always_inline unsigned long deb
  *
  * May run on IST stack.
  */
-static void handle_debug(struct pt_regs *regs, unsigned long dr6)
+static bool notify_debug(struct pt_regs *regs, unsigned long dr6)
 {
-	struct task_struct *tsk = current;
-
 	/* Store the virtualized DR6 value */
-	tsk->thread.debugreg6 = dr6;
-
-	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,
-		       SIGTRAP) == NOTIFY_STOP) {
-		return;
-	}
-
-	/* It's safe to allow irq's after DR6 has been saved */
-	cond_local_irq_enable(regs);
+	current->thread.debugreg6 = dr6;
 
-	if (v8086_mode(regs)) {
-		handle_vm86_trap((struct kernel_vm86_regs *) regs, 0,
-				 X86_TRAP_DB);
-		goto out;
-	}
-
-	/*
-	 * Reload dr6, the notifier might have changed it.
-	 */
-	dr6 = tsk->thread.debugreg6;
-	/*
-	 * If dr6 has no reason to give us about the origin of this trap,
-	 * then it's very likely the result of an icebp/int01 trap.
-	 * User wants a sigtrap for that.
-	 */
-	if (dr6 & (DR_STEP | DR_TRAP_BITS) || !dr6)
-		send_sigtrap(regs, 0, get_si_code(dr6));
+	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0, SIGTRAP) == NOTIFY_STOP)
+		return true;
 
-out:
-	cond_local_irq_disable(regs);
+	return false;
 }
 
 static __always_inline void exc_debug_kernel(struct pt_regs *regs,
@@ -872,7 +846,7 @@ static __always_inline void exc_debug_ke
 	if (!dr6)
 		goto out;
 
-	handle_debug(regs, dr6);
+	notify_debug(regs, dr6);
 
 out:
 	instrumentation_end();
@@ -902,8 +876,33 @@ static __always_inline void exc_debug_us
 	irqentry_enter_from_user_mode(regs);
 	instrumentation_begin();
 
-	handle_debug(regs, dr6);
+	if (notify_debug(regs, dr6))
+		goto out;
+
+	/*
+	 * Reload dr6, the notifier might have changed it.
+	 */
+	dr6 = current->thread.debugreg6;
+
+	/* It's safe to allow irq's after DR6 has been saved */
+	local_irq_enable();
+
+	if (v8086_mode(regs)) {
+		handle_vm86_trap((struct kernel_vm86_regs *)regs, 0, X86_TRAP_DB);
+		goto out_irq;
+	}
 
+	/*
+	 * If dr6 has no reason to give us about the origin of this trap,
+	 * then it's very likely the result of an icebp/int01 trap.
+	 * User wants a sigtrap for that.
+	 */
+	if (dr6 & (DR_STEP | DR_TRAP_BITS) || !dr6)
+		send_sigtrap(regs, 0, get_si_code(dr6));
+
+out_irq:
+	local_irq_disable();
+out:
 	instrumentation_end();
 	irqentry_exit_to_user_mode(regs);
 }