[PATCH v2 09/14] powerpc/pseries: limit machine check stack to 4GB

[Nicholas Piggin]

Christophe Leroy's on April 4, 2020 12:19 am:
> 
> 
> Le 03/04/2020 à 15:26, Nicholas Piggin a écrit :
>> This allows rtas_args to be put on the machine check stack, which
>> avoids a lot of complications with re-entrancy deadlocks.
>> 
>> Reviewed-by: Mahesh Salgaonkar <mahesh at linux.ibm.com>
>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>> ---
>>   arch/powerpc/kernel/setup_64.c | 17 ++++++++++++++++-
>>   1 file changed, 16 insertions(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
>> index e05e6dd67ae6..3a2428aa3d9a 100644
>> --- a/arch/powerpc/kernel/setup_64.c
>> +++ b/arch/powerpc/kernel/setup_64.c
>> @@ -692,6 +692,9 @@ void __init exc_lvl_early_init(void)
>>   void __init emergency_stack_init(void)
>>   {
>>   	u64 limit;
>> +#ifdef CONFIG_PPC_BOOK3S_64
> 
> #ifdef not needed, see below
> 
>> +	u64 mce_limit;
>> +#endif
>>   	unsigned int i;
>>   
>>   	/*
>> @@ -710,6 +713,18 @@ void __init emergency_stack_init(void)
>>   	 */
>>   	limit = min(ppc64_bolted_size(), ppc64_rma_size);
>>   
>> +	/*
>> +	 * Machine check on pseries calls rtas, but can't use the static
>> +	 * rtas_args due to a machine check hitting while the lock is held.
>> +	 * rtas args have to be under 4GB, so the machine check stack is
>> +	 * limited to 4GB so args can be put on stack.
>> +	 */
>> +#ifdef CONFIG_PPC_BOOK3S_64
> 
> This ifdef is not needed. FW_FEATURE_LPAR is only possible on 
> CONFIG_PPC_BOOK3S_64 (indeed only on PSERIES or PS3). On others 
> firmware_has_feature(FW_FEATURE_LPAR) should return 0 at compile time.

Sure I'll remove it.

>> +	mce_limit = limit;
>> +	if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > 4UL*1024*1024*1024)
>> +		mce_limit = 4UL*1024*1024*1024;
> 
> You should use SZ_4G instead of hardcoding.

Will do.

Thanks,
Nick