Re: [PATCH v3 2/2] powerpc/rtas: Implement reentrant rtas call

[Nathan Lynch <nathanl@linux.ibm.com>]

Hi,

Leonardo Bras <leobras.c@gmail.com> writes:
> +/**
> + * rtas_call_reentrant() - Used for reentrant rtas calls
> + * @token:	Token for desired reentrant RTAS call
> + * @nargs:	Number of Input Parameters
> + * @nret:	Number of Output Parameters
> + * @outputs:	Array of outputs
> + * @...:	Inputs for desired RTAS call
> + *
> + * According to LoPAR documentation, only "ibm,int-on", "ibm,int-off",
> + * "ibm,get-xive" and "ibm,set-xive" are currently reentrant.
> + * Reentrant calls need their own rtas_args buffer, so not using rtas.args, but
> + * PACA one instead.
> + *
> + * Return:	-1 on error,
> + *		First output value of RTAS call if (nret > 0),
> + *		0 otherwise,
> + */
> +
> +int rtas_call_reentrant(int token, int nargs, int nret, int *outputs, ...)
> +{
> +	va_list list;
> +	struct rtas_args *args;
> +	int i;
> +
> +	if (!rtas.entry || token == RTAS_UNKNOWN_SERVICE)
> +		return -1;
> +
> +	/* We use the per-cpu (PACA) rtas args buffer */
> +	args = &local_paca->reentrant_args;
> +
> +	va_start(list, outputs);
> +	va_rtas_call_unlocked(args, token, nargs, nret, list);
> +	va_end(list);
> +
> +	if (nret > 1 && outputs)
> +		for (i = 0; i < nret - 1; ++i)
> +			outputs[i] = be32_to_cpu(args->rets[i + 1]);

Doesn't this need to be more careful about preemption and exceptions?
I.e. the args structure in the paca needs to be protected from
concurrent use somehow, like any per-cpu data structure.

local_irq_save/restore while accessing local_paca->reentrant_args here
would be sufficient I think?