linux-kernel - [PATCH 11/13] x86/debug: Simplify hw_breakpoint

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Date:   Wed, 02 Sep 2020 15:26:00 +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>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 11/13] x86/debug: Simplify hw_breakpoint_handler()

This is called with interrupts disabled, there's no point in using
get_cpu() and per_cpu().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/hw_breakpoint.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -487,7 +487,7 @@ EXPORT_SYMBOL_GPL(hw_breakpoint_restore)
  */
 static int hw_breakpoint_handler(struct die_args *args)
 {
-	int i, cpu, rc = NOTIFY_STOP;
+	int i, rc = NOTIFY_STOP;
 	struct perf_event *bp;
 	unsigned long dr6;
 	unsigned long *dr6_p;
@@ -505,12 +505,10 @@ static int hw_breakpoint_handler(struct
 		return NOTIFY_DONE;
 
 	/*
-	 * Assert that local interrupts are disabled
 	 * Reset the DRn bits in the virtualized register value.
 	 * The ptrace trigger routine will add in whatever is needed.
 	 */
 	current->thread.debugreg6 &= ~DR_TRAP_BITS;
-	cpu = get_cpu();
 
 	/* Handle all the breakpoints that were triggered */
 	for (i = 0; i < HBP_NUM; ++i) {
@@ -525,7 +523,7 @@ static int hw_breakpoint_handler(struct
 		 */
 		rcu_read_lock();
 
-		bp = per_cpu(bp_per_reg[i], cpu);
+		bp = this_cpu_read(bp_per_reg[i]);
 		/*
 		 * Reset the 'i'th TRAP bit in dr6 to denote completion of
 		 * exception handling
@@ -560,8 +558,6 @@ static int hw_breakpoint_handler(struct
 	    (dr6 & (~DR_TRAP_BITS)))
 		rc = NOTIFY_DONE;
 
-	put_cpu();
-
 	return rc;
 }