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 18:42:14 +0200
From:	leroy christophe <christophe.leroy@....fr>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Paul Mackerras <paulus@...ba.org>, scottwood@...escale.com
Subject: Re: [PATCH v3 03/21] powerpc/8xx: exception InstructionAccess does
 not exist on MPC8xx


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(-)
>>
>> diff --git a/arch/powerpc/kernel/head_8xx.S
> b/arch/powerpc/kernel/head_8xx.S
>> index 3af6db1..fbe5d10 100644
>> --- a/arch/powerpc/kernel/head_8xx.S
>> +++ b/arch/powerpc/kernel/head_8xx.S
>> @@ -234,15 +234,9 @@ 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)
>> +   EXCEPTION(0x400, InstructionAccess, unknown_exception, EXC_XFER_STD)
>>
>>   /* External interrupt */
>>      EXCEPTION(0x500, HardwareInterrupt, do_IRQ, EXC_XFER_LITE)
>> @@ -382,7 +376,7 @@ InstructionTLBMiss:
>>   #endif
>>      mfspr   r10, SPRN_SPRG_SCRATCH2
>>      EXCEPTION_EPILOG_0
>> -   b   InstructionAccess
>> +   b   InstructionTLBError
>>
>>      . = 0x1200
>>   DataStoreTLBMiss:
>> @@ -477,7 +471,10 @@ DataStoreTLBMiss:
>>    */
>>      . = 0x1300
>>   InstructionTLBError:
>> -   b   InstructionAccess
>> +   EXCEPTION_PROLOG
>> +   mr   r4,r12
>> +   mr   r5,r9
>> +   EXC_XFER_LITE(0x1300, handle_page_fault)
> 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 ?

@@ -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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