Subject: Re: [PATCH] powerpc64/hw_breakpoints: Handle data breakpoints in radix mode

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 14 Jun 2017 08:38:43 +0530

"Naveen N. Rao" <[email-masked]> writes:

> On P9, 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(). Move this check to handle_page_fault() so as to catch
> data breakpoints in both hash and radix MMU modes.
>
> While at it, also remove the label '11' that was made redundant by
> commit a546498f3bf9aa ("powerpc: Call do_page_fault() with interrupts
> off")
>
> (*)
>     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
>     current = 0xc0000000f1f59700
>     paca    = 0xc00000000fd40000 softe: 0 irq_happened: 0x01
>     pid   = 1192, comm = sh
>     Linux version 4.12.0-rc3-nnr (root@ea605ec2993c) (gcc version 5.4.0 20160609 (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.1) ) #74 SMP Tue Jun 13 16:52:49 UTC 2017
>     enter ? for help
>     [c0000000ef1e7dc0] c000000000116ac4 find_task_by_vpid+0x44/0x90
>     [c0000000ef1e7de0] c000000000108800 SyS_setpgid+0x80/0x220
>     [c0000000ef1e7e30] c00000000000ba6c system_call+0x38/0xfc
>     --- Exception: c01 (System Call) at 00007fff94480890
>     SP (7fffd91e7260) is in userspace
>
> Fixes: caca285e5ab4a ("powerpc/mm/radix: Use STD_MMU_64 to properly
> isolate hash related code")
> Reported-by: Shriya R. Kulkarni <[email-masked]>
> Signed-off-by: Naveen N. Rao <[email-masked]>
> ---
>  arch/powerpc/kernel/exceptions-64s.S | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index ae418b85c17c..17ee701b8336 100644
> --- 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? */

Can we convert that to a #define value. Ram did try to do that here.

https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-June/158607.html

>  	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) */
> @@ -1442,7 +1440,9 @@ do_hash_page:
>  
>  /* Here we have a page fault that hash_page can't handle. */
>  handle_page_fault:
> -11:	ld	r4,_DAR(r1)
> +	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
> -- 
> 2.12.2

-aneesh