Re: [PATCH] poewrpc/mce: Fix SLB rebolting during MCE recovery path.

[Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>]

On 08/21/2018 03:57 PM, Nicholas Piggin wrote:
> On Fri, 17 Aug 2018 14:51:47 +0530
> Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:
> 
>> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>>
>> With the powrpc next commit e7e81847478 (poewrpc/mce: Fix SLB rebolting
>> during MCE recovery path.), the SLB error recovery is broken. The
>> commit missed a crucial change of OR-ing index value to RB[52-63] which
>> selects the SLB entry while rebolting. This patch fixes that.
>>
>> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>  arch/powerpc/mm/slb.c |    5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
>> index 0b095fa54049..6dd9913425bc 100644
>> --- a/arch/powerpc/mm/slb.c
>> +++ b/arch/powerpc/mm/slb.c
>> @@ -101,9 +101,12 @@ void __slb_restore_bolted_realmode(void)
>>  
>>  	 /* No isync needed because realmode. */
>>  	for (index = 0; index < SLB_NUM_BOLTED; index++) {
>> +		unsigned long rb = be64_to_cpu(p->save_area[index].esid);
>> +
>> +		rb = (rb & ~0xFFFul) | index;
>>  		asm volatile("slbmte  %0,%1" :
>>  		     : "r" (be64_to_cpu(p->save_area[index].vsid)),
>> -		       "r" (be64_to_cpu(p->save_area[index].esid)));
>> +		       "r" (rb));
>>  	}
>>  }
>>  
>>
> 
> I'm just looking at this again. The bolted save areas do have the
> index field set. So for the OS, your patch should be equivalent to
> this, right?
> 
>  static inline void slb_shadow_clear(enum slb_index index)
>  {
> -       WRITE_ONCE(get_slb_shadow()->save_area[index].esid, 0);
> +       WRITE_ONCE(get_slb_shadow()->save_area[index].esid, index);
>  }
> 
> Which seems like a better fix.

Yeah this also fixes the issue. The only additional change required is
cpu_to_be64(index). As long as we maintain index in bolted save areas
(for valid/invalid entries) we should be ok. Will respin v2 with this
change.

Thanks,
-Mahesh.