linux-kernel - Re: [PATCH v3 03/21] powerpc/8xx: exception InstructionAccess does not exist on MPC8xx

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Date:	Thu, 18 Sep 2014 20:52:14 +0200
From:	christophe leroy <christophe.leroy@....fr>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
CC:	scottwood@...escale.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH v3 03/21] powerpc/8xx: exception InstructionAccess does
 not exist on MPC8xx


Le 18/09/2014 18:42, leroy christophe a écrit :
>
> Le 18/09/2014 17:15, Joakim Tjernlund a écrit :
>> Christophe Leroy <christophe.leroy@....fr> wrote on 2014/09/17 18:36:57:
>>> Exception InstructionAccess does not exist on MPC8xx. No need to branch
>> there from somewhere else.
>>> Handling can be done directly in InstructionTLBError Exception.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>>>
>>> ---
>>> Changes in v2:
>>> - None
>>>
>>> Changes in v3:
>>> - arch/powerpc/mm/fault.c uses the vector number, so make sure it
>> understand
>>> the new ones.
>>>
>>>   arch/powerpc/kernel/head_8xx.S | 17 +++++++----------
>>>   arch/powerpc/mm/fault.c        |  1 +
>>>   2 files changed, 8 insertions(+), 10 deletions(-)
[...]
>>> Still don't like that you change the vector number, every other ppc 
>>> uses
>> the
>> standard number.
>>
>> Can you not just lie here(EXC_XFER_LITE(0x400, handle_page_fault))?
>> Move the code to InstructionAccess too and let TLBError branch there.
> My issue was that if I do EXC_XFER_LITE(0x400, handle_page_fault), I 
> can't leave the
>     EXCEPTION(0x400, InstructionAccess, unknown_exception, 
> EXC_XFER_STD) at address .400
> Otherwise, I get twice the same label.
>
> What about the following patch then ? Would this be acceptable ?
I don't like what I propose two hours ago indeed.
Is it really worth trying to implement code for vectors 0x300 and 0x400 
which are clearly stated in the Reference Manual as never being 
generated by the HW ?.
If I just don't put anything at 0x300 and 0x400 is that OK ?
Otherwise I have to put some code that will branch to TLBerror code, but 
writing dead code doesn't enchant me.

Christophe
>
> @@ -234,15 +234,13 @@ DataAccess:
>      EXC_XFER_LITE(0x300, handle_page_fault)
>
>  /* Instruction access exception.
> - * This is "never generated" by the MPC8xx.  We jump to it for other
> - * translation errors.
> + * This is "never generated" by the MPC8xx.
>   */
>      . = 0x400
>  InstructionAccess:
>      EXCEPTION_PROLOG
> -    mr    r4,r12
> -    mr    r5,r9
> -    EXC_XFER_LITE(0x400, handle_page_fault)
> +    addi    r3,r1,STACK_FRAME_OVERHEAD
> +    EXC_XFER_STD(0x401, unknown_exception)
>
>  /* External interrupt */
>      EXCEPTION(0x500, HardwareInterrupt, do_IRQ, EXC_XFER_LITE)
> @@ -382,7 +380,7 @@ InstructionTLBMiss:
>  #endif
>      mfspr    r10, SPRN_SPRG_SCRATCH2
>      EXCEPTION_EPILOG_0
> -    b    InstructionAccess
> +    b    InstructionTLBError
>
>      . = 0x1200
>  DataStoreTLBMiss:
> @@ -477,7 +475,11 @@ DataStoreTLBMiss:
>   */
>      . = 0x1300
>  InstructionTLBError:
> -    b    InstructionAccess
> +    EXCEPTION_PROLOG
> +    mr    r4,r12
> +    mr    r5,r9
> +    /* 0x400 is InstructionAccess exception, needed by 
> bad_page_fault() */
> +    EXC_XFER_LITE(0x400, handle_page_fault)
>
>  /* This is the data TLB error on the MPC8xx.  This could be due to
>   * many reasons, including a dirty update to a pte.  We can catch that
>
>
>>
>> If not I think you should keep the old/current way?
>>
>> Same for DataTLB Miss/Error
>>
>>>   /* This is the data TLB error on the MPC8xx.  This could be due to
>>>    * many reasons, including a dirty update to a pte.  We can catch 
>>> that
>>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>>> index 51ab9e7..4d63c96 100644
>>> --- a/arch/powerpc/mm/fault.c
>>> +++ b/arch/powerpc/mm/fault.c
>>> @@ -526,6 +526,7 @@ void bad_page_fault(struct pt_regs *regs, unsigned
>> long address, int sig)
>>>         break;
>>>      case 0x400:
>>>      case 0x480:
>>> +   case 0x1300:
>>>         printk(KERN_ALERT "Unable to handle kernel paging request for "
>>>            "instruction fetch\n");
>>>         break;
>>> -- 
>>> 2.1.0
>>>
>


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