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Date: Fri, 27 Mar 2020 10:54:30 +0530
From: Mahesh J Salgaonkar <mahesh@linux.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v2 08/12] powerpc/pseries: limit machine check stack to 4GB
References: <20200325103410.157573-1-npiggin@gmail.com>
 <20200325103410.157573-9-npiggin@gmail.com>
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Reply-To: mahesh@linux.ibm.com
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
 Ganesh Goudar <ganeshgr@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

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.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kernel/setup_64.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> 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;
> 
>  	/*
> @@ -713,6 +716,16 @@ 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.
> +	 */
> +	mce_limit = limit;
> +	if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > 4UL*1024*1024*1024)
> +		mce_limit = 4UL*1024*1024*1024;
> +

Don't you need this as well under CONFIG_PPC_BOOK3S_64 #ifdef ??

Rest looks good.

Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>

Thanks,
-Mahesh.