-----Original Message-----
From: Wood Scott-B07421
Sent: Thursday, May 16, 2013 10:24 PM
To: Bhushan Bharat-R65777
Cc: galak@kernel.crashing.org; benh@kernel.crashing.org; linuxppc-
dev@lists.ozlabs.org; Yoder Stuart-B08248; Yang James-RA8135; Bhushan Bha=

rat-

R65777
Subject: Re: [PATCH 2/2 v2] powerpc: restore dbcr0 on user space exit
=20
On 05/16/2013 12:34:32 AM, Bharat Bhushan wrote:

quoted

On BookE (Branch taken + Single Step) is as same as Branch Taken on
BookS and in Linux we simulate BookS behavior for BookE as well.
When doing so, in Branch taken handling we want to set DBCR0_IC but we
update the current->thread->dbcr0 and not DBCR0.

Now on 64bit the current->thread.dbcr0 (and other debug registers) is
synchronized ONLY on context switch flow. But after handling Branch
taken in debug exception if we return back to user space without
context switch then single stepping change (DBCR0_ICMP) does not get
written in h/w DBCR0 and Instruction Complete exception does not
happen.

This fixes using ptrace reliably on BookE-PowerPC

Signed-off-by: Bharat Bhushan <redacted>
---
v1->v2
 - Subject line was not having 2/2

 arch/powerpc/kernel/asm-offsets.c |    1 +
 arch/powerpc/kernel/entry_64.S    |   24 ++++++++++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/asm-offsets.c

b/arch/powerpc/kernel/asm-offsets.c
index b51a97c..1e2f450 100644

--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c

@@ -103,6 +103,7 @@ int main(void)
 #endif /* CONFIG_VSX */
 #ifdef CONFIG_PPC64
 	DEFINE(KSP_VSID, offsetof(struct thread_struct, ksp_vsid));
+	DEFINE(THREAD_DBCR0, offsetof(struct thread_struct, dbcr0));
 #else /* CONFIG_PPC64 */
 	DEFINE(PGDIR, offsetof(struct thread_struct, pgdir));  #if

defined(CONFIG_4xx) || defined(CONFIG_BOOKE) diff --git
a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 794889b..561630d 100644

--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S

@@ -614,7 +614,9 @@ _GLOBAL(ret_from_except_lite)
 	 * from the interrupt.
 	 */
 #ifdef CONFIG_PPC_BOOK3E
+	ld	r3,PACACURRENT(r13)
 	wrteei	0
+	lwz	r10,(THREAD+THREAD_DBCR0)(r3)

=20
I know I asked you to move these earlier, but this is probably too early.=

..

wrteei has synchronization, so it will probably have to wait until the ld
completes, defeating the purpose of moving it earlier.
=20
Ideal would probably be to load PACACURRENT immediately after _MSR(r1), a=

nd load

DBCR0 just after "beq resume_kernel".

ok

=20
Or, move DBCR0 to therad_info as I suggested internally.

If no one have objection on moving dbcr0 to thread_info then I am happy to =
do that.

=20
Regardless of what you do, could you run a basic syscall benchmark (e.g. =

from

lmbench) before and after the patch?

Sure.

-Bharat

=20
-Scott