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Date: Fri, 03 Apr 2020 20:24:07 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v2 08/12] powerpc/pseries: limit machine check stack to 4GB
To: mahesh@linux.ibm.com
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Cc: linuxppc-dev@lists.ozlabs.org, Ganesh Goudar <ganeshgr@linux.ibm.com>,
 Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
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Mahesh J Salgaonkar's on March 27, 2020 3:24 pm:
> On 2020-03-25 20:34:06 Wed, Nicholas Piggin wrote:
>> This allows rtas_args to be put on the machine check stack, which
>> avoids a lot of complications with re-entrancy deadlocks.
>>=20
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>  arch/powerpc/kernel/setup_64.c | 15 ++++++++++++++-
>>  1 file changed, 14 insertions(+), 1 deletion(-)
>>=20
>> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_=
64.c
>> index 3bf03666ee09..ca1041f8a578 100644
>> --- a/arch/powerpc/kernel/setup_64.c
>> +++ b/arch/powerpc/kernel/setup_64.c
>> @@ -695,6 +695,9 @@ void __init exc_lvl_early_init(void)
>>  void __init emergency_stack_init(void)
>>  {
>>  	u64 limit;
>> +#ifdef CONFIG_PPC_BOOK3S_64
>> +	u64 mce_limit;
>> +#endif
>>  	unsigned int i;
>>=20
>>  	/*
>> @@ -713,6 +716,16 @@ void __init emergency_stack_init(void)
>>  	 */
>>  	limit =3D min(ppc64_bolted_size(), ppc64_rma_size);
>>=20
>> +	/*
>> +	 * 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.
>> +	 */
>> +	mce_limit =3D limit;
>> +	if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > 4UL*1024*1024=
*1024)
>> +		mce_limit =3D 4UL*1024*1024*1024;
>> +
>=20
> Don't you need this as well under CONFIG_PPC_BOOK3S_64 #ifdef ??

Good catch.

Thanks,
Nick
=