linux-kernel - [RFC][PATCH 6/7] x86/debug: Simplify #DB signal code

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Message-ID: <20200820104905.411406337@infradead.org>
Date:   Thu, 20 Aug 2020 12:38:38 +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 6/7] x86/debug: Simplify #DB signal code


Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/traps.c |   23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -786,15 +786,6 @@ static __always_inline unsigned long deb
 static void handle_debug(struct pt_regs *regs, unsigned long dr6)
 {
 	struct task_struct *tsk = current;
-	bool user_icebp;
-	int si_code;
-
-	/*
-	 * 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.
-	 */
-	user_icebp = !dr6;
 
 	/* Store the virtualized DR6 value */
 	tsk->thread.debugreg6 = dr6;
@@ -813,9 +804,17 @@ static void handle_debug(struct pt_regs
 		goto out;
 	}
 
-	si_code = get_si_code(tsk->thread.debugreg6);
-	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
-		send_sigtrap(regs, 0, si_code);
+	/*
+	 * 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));
 
 out:
 	cond_local_irq_disable(regs);