[SRU][Zesty][PATCH 1/1] powerpc/64s: Handle data breakpoints in Radix mode

Joseph Salisbury joseph.salisbury at canonical.com
Wed Sep 27 15:32:41 UTC 2017

From: "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1706033

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.

Fixes: caca285e5ab4 ("powerpc/mm/radix: Use STD_MMU_64 to properly isolate hash related code")
Cc: stable at vger.kernel.org # v4.7+
Reported-by: Shriya R. Kulkarni <shriykul at in.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
[mpe: Fix the fall-through case on hash, we need to reload DSISR]
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

(cherry picked from commit d89ba5353f301971dd7d2f9fdf25c4432728f38e)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
 arch/powerpc/kernel/exceptions-64s.S | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 7845613..fa2c6c9 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1418,10 +1418,8 @@ USE_TEXT_SECTION()
-	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 at h
-	bne-    handle_dabr_fault
 	lwz	r0,TI_PREEMPT(r11)	/* If we're in an "NMI" */
 	andis.	r0,r0,NMI_MASK at h	/* (i.e. an irq when soft-disabled) */
@@ -1445,11 +1443,16 @@ 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. */
-11:	ld	r4,_DAR(r1)
+11:	andis.  r0,r4,DSISR_DABRMATCH at h
+	bne-    handle_dabr_fault
+	ld	r4,_DAR(r1)
 	ld	r5,_DSISR(r1)
 	bl	do_page_fault

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