linux-kernel - [PATCH v2 1/4] kprobes/powerpc: Do not disable External interrupts during single step

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Date:	Mon, 03 Dec 2012 20:37:42 +0530
From:	"Suzuki K. Poulose" <suzuki@...ibm.com>
To:	bigeasy@...utronix.de, oleg@...hat.com, ananth@...ibm.com,
	srikar@...ux.vnet.ibm.com
Cc:	peterz@...radead.org, benh@...nel.crashing.org,
	Kumar Gala <galak@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	anton@...hat.com, mingo@...e.hu
Subject: [PATCH v2 1/4] kprobes/powerpc: Do not disable External interrupts
 during single step

From: Suzuki K. Poulose <suzuki@...ibm.com>

External/Decrement exceptions have lower priority than the Debug Exception.
So, we don't have to disable the External interrupts before a single step.
However, on BookE, Critical Input Exception(CE) has higher priority than a
Debug Exception. Hence we mask them.

Signed-off-by: 	Suzuki K. Poulose <suzuki@...ibm.com>
Cc:		Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:		Ananth N Mavinakaynahalli <ananth@...ibm.com>
Cc:		Kumar Gala <galak@...nel.crashing.org>
Cc:		linuxppc-dev@...abs.org
---
 arch/powerpc/kernel/kprobes.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index e88c643..4901b34 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -104,13 +104,13 @@ void __kprobes arch_remove_kprobe(struct kprobe *p)
 
 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
-	/* We turn off async exceptions to ensure that the single step will
-	 * be for the instruction we have the kprobe on, if we dont its
-	 * possible we'd get the single step reported for an exception handler
-	 * like Decrementer or External Interrupt */
-	regs->msr &= ~MSR_EE;
 	regs->msr |= MSR_SINGLESTEP;
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
+	/* 
+	 * We turn off Critical Input Exception(CE) to ensure that the single
+	 * step will be for the instruction we have the probe on; if we don't,
+	 * it is possible we'd get the single step reported for CE.
+	 */
 	regs->msr &= ~MSR_CE;
 	mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
 #ifdef CONFIG_PPC_47x

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