Re: [PATCH v3 09/15] powerpc/pseries: limit machine check stack to 4GB

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 07/04/2020 à 07:16, 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@linux.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>

> ---
>   arch/powerpc/kernel/setup_64.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 438a9befce41..defe05b6b7a9 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -709,7 +709,7 @@ void __init exc_lvl_early_init(void)
>    */
>   void __init emergency_stack_init(void)
>   {
> -	u64 limit;
> +	u64 limit, mce_limit;
>   	unsigned int i;
>   
>   	/*
> @@ -726,7 +726,16 @@ void __init emergency_stack_init(void)
>   	 * initialized in kernel/irq.c. These are initialized here in order
>   	 * to have emergency stacks available as early as possible.
>   	 */
> -	limit = min(ppc64_bolted_size(), ppc64_rma_size);
> +	limit = mce_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.
> +	 */
> +	if (firmware_has_feature(FW_FEATURE_LPAR) && mce_limit > SZ_4G)
> +		mce_limit = SZ_4G;
>   
>   	for_each_possible_cpu(i) {
>   		paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;
> @@ -736,7 +745,7 @@ 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
>   	}
>   }
>