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

[Christophe Leroy]

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.

> +	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.

> +#endif
> +
>   	for_each_possible_cpu(i) {
>   		paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
>   
> @@ -718,7 +733,7 @@ void __init emergency_stack_init(void)
>   		paca_ptrs[i]->nmi_emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
>   
>   		/* emergency stack for machine check exception handling. */
> -		paca_ptrs[i]->mc_emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
> +		paca_ptrs[i]->mc_emergency_sp = alloc_stack(mce_limit, i) + THREAD_SIZE;
>   #endif
>   	}
>   }
> 

Christophe