linux-kernel - [tip: x86/entry] x86/debug: Simplify #DB signal code

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Date:   Fri, 04 Sep 2020 13:16:09 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/entry] x86/debug: Simplify #DB signal code

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

Commit-ID:     4182e9436916a48f16207f0619562f1d3843a0c8
Gitweb:        https://git.kernel.org/tip/4182e9436916a48f16207f0619562f1d3843a0c8
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 02 Sep 2020 15:25:55 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 04 Sep 2020 15:12:52 +02:00

x86/debug: Simplify #DB signal code

There's no point in calculating si_code if it's not going to be used.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Daniel Thompson <daniel.thompson@...aro.org>
Link: https://lore.kernel.org/r/20200902133200.967434217@infradead.org

---
 arch/x86/kernel/traps.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 58bc434..24e09f8 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -786,15 +786,14 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
 static void handle_debug(struct pt_regs *regs, unsigned long dr6)
 {
 	struct task_struct *tsk = current;
-	bool user_icebp;
-	int si_code;
+	bool icebp;
 
 	/*
 	 * 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;
+	icebp = !dr6;
 
 	/* Store the virtualized DR6 value */
 	tsk->thread.debugreg6 = dr6;
@@ -813,6 +812,11 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6)
 		goto out;
 	}
 
+	/*
+	 * Reload dr6, the notifier might have changed it.
+	 */
+	dr6 = tsk->thread.debugreg6;
+
 	if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
 		/*
 		 * Historical junk that used to handle SYSENTER single-stepping.
@@ -825,9 +829,8 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6)
 		regs->flags &= ~X86_EFLAGS_TF;
 	}
 
-	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);
+	if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
+		send_sigtrap(regs, 0, get_si_code(dr6));
 
 out:
 	cond_local_irq_disable(regs);