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

Stefan Bader stefan.bader at canonical.com
Wed Sep 27 19:19:06 UTC 2017


On 27.09.2017 11:32, Joseph Salisbury wrote:
> 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>
Acked-by: Stefan Bader <stefan.bader 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()
>  	.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 at 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 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. */
>  handle_page_fault:
> -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)
>  	addi	r3,r1,STACK_FRAME_OVERHEAD
>  	bl	do_page_fault
> 


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