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Date:	Fri, 18 Jul 2014 14:10:49 +0200
From:	Jiri Slaby <>
	Michael Ellerman <>,
	Benjamin Herrenschmidt <>,
	Jiri Slaby <>
Subject: [PATCH 3.12 044/170] powerpc/perf: Ensure all EBB register state is cleared on fork()

From: Michael Ellerman <>

3.12-stable review patch.  If anyone has any objections, please let me know.


commit 3df48c981d5a9610e02e9270b1bc4274fb536710 upstream.

In commit 330a1eb "Core EBB support for 64-bit book3s" I messed up
clear_task_ebb(). It clears some but not all of the task's Event Based
Branch (EBB) registers when we duplicate a task struct.

That allows a child task to observe the EBBHR & EBBRR of its parent,
which it should not be able to do.

Fix it by clearing EBBHR & EBBRR.

Signed-off-by: Michael Ellerman <>
Signed-off-by: Benjamin Herrenschmidt <>
Signed-off-by: Jiri Slaby <>
 arch/powerpc/include/asm/switch_to.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 2be5618cdec6..06d63a3c1a88 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -85,6 +85,8 @@ static inline void clear_task_ebb(struct task_struct *t)
 #ifdef CONFIG_PPC_BOOK3S_64
     /* EBB perf events are not inherited, so clear all EBB state. */
+    t->thread.ebbrr = 0;
+    t->thread.ebbhr = 0;
     t->thread.bescr = 0;
     t->thread.mmcr2 = 0;
     t->thread.mmcr0 = 0;

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