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

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On Wednesday 14 June 2017 10:41 AM, Naveen N. Rao wrote:
> Hi Aneesh,
> 
> On 2017/06/14 08:38AM, Aneesh Kumar K.V wrote:
>> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> 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 <shriykul@in.ibm.com>
>>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>>> ---
>>>   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
> 
> Hmm... I feel it will be good to do that as part of Ram's series since
> he has already coded it up :)
> 
> Ram's patches will anyway require a rebase and the change I do here for
> detecting DAWR already has a #define, so it should be a simple matter of
> including DSISR_DABRMATCH in DSISR_PAGE_FAULT_MASK.
> 
> But, if you really feel that I should make that change here, please do
> let me know and I will re-spin with those changes.
> 

The thing is that change from 0xa410 to 0xa450 is not clear at all. And 
it needs proper documentation. IMHO the best way to do that is switch to 
#define name for that constant.

-aneesh