powerpc/64s: Handle data breakpoints in Radix mode

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@vger.kernel.org # v4.7+
Reported-by: Shriya R. Kulkarni <shriykul@in.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
[mpe: Fix the fall-through case on hash, we need to reload DSISR]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index ae418b8..b886795 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1411,10 +1411,8 @@ USE_TEXT_SECTION()
        .balign IFETCH_ALIGN_BYTES
 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