Patch "powerpc/64s: Handle data breakpoints in Radix mode" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/64s: Handle data breakpoints in Radix mode

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-64s-handle-data-breakpoints-in-radix-mode.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Naveen N. Rao" <[email protected]>
Date: Wed, 14 Jun 2017 00:12:00 +0530
Subject: powerpc/64s: Handle data breakpoints in Radix mode

From: Naveen N. Rao <[email protected]>

commit d89ba5353f301971dd7d2f9fdf25c4432728f38e upstream.

On Power9, trying to use data breakpoints throws the splat shown below. This is because the check for a data breakpoint in DSISR is in do_hash_page(), which is not called when in Radix mode.

  Unable to handle kernel paging request for data at address 0xc000000000e19218
  Faulting instruction address: 0xc0000000001155e8
  cpu 0x0: Vector: 300 (Data Access) at [c0000000ef1e7b20]
  pc: c0000000001155e8: find_pid_ns+0x48/0xe0
  lr: c000000000116ac4: find_task_by_vpid+0x44/0x90
  sp: c0000000ef1e7da0
  msr: 9000000000009033
  dar: c000000000e19218
  dsisr: 400000

Move the check to handle_page_fault() so as to catch data breakpoints in both Hash and Radix MMU modes.

We have to change the check in do_hash_page() against 0xa410 to use 0xa450, so as to include the value of (DSISR_DABRMATCH << 16).

There are two sites that call handle_page_fault() when in Radix, both already pass DSISR in r4.

---
 arch/powerpc/kernel/exceptions-64s.S |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

@@ -1411,10 +1411,8 @@ USE_TEXT_SECTION()
 	.align	7
 do_hash_page:
 #ifdef CONFIG_PPC_STD_MMU_64
-	andis.	r0,r4,0xa410		/* weird error? */
+	andis.	r0,r4,0xa450		/* weird error? */
 	bne-	handle_page_fault	/* if not, try to insert a HPTE */
-	andis.  r0,r4,DSISR_DABRMATCH@h
-	bne-    handle_dabr_fault
 	CURRENT_THREAD_INFO(r11, r1)
 	lwz	r0,TI_PREEMPT(r11)	/* If we're in an "NMI" */
 	andis.	r0,r0,NMI_MASK@h	/* (i.e. an irq when soft-disabled) */

@@ -1438,11 +1436,16 @@ do_hash_page:
 
 	/* Error */
 	blt-	13f
+
+	/* Reload DSISR into r4 for the DABR check below */
+	ld      r4,_DSISR(r1)
 #endif /* CONFIG_PPC_STD_MMU_64 */
 
 /* Here we have a page fault that hash_page can't handle. */
 handle_page_fault:
-11:	ld	r4,_DAR(r1)
+11:	andis.  r0,r4,DSISR_DABRMATCH@h
+	bne-    handle_dabr_fault
+	ld	r4,_DAR(r1)
 	ld	r5,_DSISR(r1)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_page_fault

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/powerpc-kprobes-pause-function_graph-tracing-during-jprobes-handling.patch queue-4.9/powerpc-64s-handle-data-breakpoints-in-radix-mode.patch queue-4.9/powerpc-perf-fix-oops-when-kthread-execs-user-process.patch