Subject: Re: [RFC PATCH 1/9] powerpc/pseries: add cpu DLPAR support for drc-info property

From: Nathan Lynch <[email-masked]>
Date: Thu, 10 Oct 2019 13:56:28 -0500

Hi Tyrel,

Tyrel Datwyler <[email-masked]> writes:
> +static bool valid_cpu_drc_index(struct device_node *parent, u32 drc_index)
> +{
> +	const __be32 *indexes;
> +	int i;
> +
> +	if (of_find_property(parent, "ibm,drc-info", NULL))
> +		return drc_info_valid_index(parent, drc_index);
> +
> +	indexes = of_get_property(parent, "ibm,drc-indexes", NULL);
> +	if (!indexes)
> +		return false;
> +
> +	for (i = 0; i < indexes[0]; i++) {

should this be:

        for (i = 0; i < be32_to_cpu(indexes[0]); i++) {
?

> +		if (be32_to_cpu(indexes[i + 1]) == drc_index)
> +			return true;
> +	}
> +
> +	return false;
>  }

It looks like this rewrites valid_cpu_drc_index()'s existing code for
parsing ibm,drc-indexes but I don't see the need for this.

This patch would be easier to review if that were dropped or split out.

>  
>  static ssize_t dlpar_cpu_add(u32 drc_index)
> @@ -720,8 +756,11 @@ static int dlpar_cpu_remove_by_count(u32 cpus_to_remove)
>  static int find_dlpar_cpus_to_add(u32 *cpu_drcs, u32 cpus_to_add)
>  {
>  	struct device_node *parent;
> +	struct property *info;
> +	const __be32 *indexes;
>  	int cpus_found = 0;
> -	int index, rc;
> +	int i, j;
> +	u32 drc_index;
>  
>  	parent = of_find_node_by_path("/cpus");
>  	if (!parent) {
> @@ -730,24 +769,46 @@ static int find_dlpar_cpus_to_add(u32 *cpu_drcs, u32 cpus_to_add)
>  		return -1;
>  	}
>  
> -	/* Search the ibm,drc-indexes array for possible CPU drcs to
> -	 * add. Note that the format of the ibm,drc-indexes array is
> -	 * the number of entries in the array followed by the array
> -	 * of drc values so we start looking at index = 1.
> -	 */
> -	index = 1;
> -	while (cpus_found < cpus_to_add) {
> -		u32 drc;
> +	info = of_find_property(parent, "ibm,drc-info", NULL);
> +	if (info) {
> +		struct of_drc_info drc;
> +		const __be32 *value;
> +		int count;
>  
> -		rc = of_property_read_u32_index(parent, "ibm,drc-indexes",
> -						index++, &drc);
> -		if (rc)
> -			break;
> +		value = of_prop_next_u32(info, NULL, &count);
> +		if (value)
> +			value++;
>  
> -		if (dlpar_cpu_exists(parent, drc))
> -			continue;
> +		for (i = 0; i < count; i++) {
> +			of_read_drc_info_cell(&info, &value, &drc);
> +			if (strncmp(drc.drc_type, "CPU", 3))
> +				break;
> +
> +			for (j = 0; j < drc.num_sequential_elems; j++) {
> +				drc_index = drc.drc_index_start + (drc.sequential_inc * j);
> +
> +				if (dlpar_cpu_exists(parent, drc_index))
> +					continue;
>  
> -		cpu_drcs[cpus_found++] = drc;
> +				cpu_drcs[cpus_found++] = drc_index;

I am failing to see how this loop is limited by the cpus_to_add
parameter as it was before this change. It looks like this will overflow
the cpu_drcs array when cpus_to_add is less than the number of cpus
found.

As an aside I don't understand how the add_by_count()/dlpar_cpu_exists()
algorithm could be correct as it currently stands. It seems to pick the
first X indexes for which a corresponding cpu node is absent, but that
set of indexes does not necessarily match the set that is available to
configure. Something to address separately I suppose.

> +			}
> +		}
> +	} else {
> +		indexes = of_get_property(parent, "ibm,drc-indexes", NULL);
> +
> +		/* Search the ibm,drc-indexes array for possible CPU drcs to
> +	 	* add. Note that the format of the ibm,drc-indexes array is
> +	 	* the number of entries in the array followed by the array
> +	 	* of drc values so we start looking at index = 1.
> +	 	*/
> +		for (i = 1; i < indexes[0]; i++) {
> +			drc_index = be32_to_cpu(indexes[i]);
> +
> +			if (dlpar_cpu_exists(parent, drc_index))
> +				continue;
> +
> +			cpu_drcs[cpus_found++] = drc_index;
> +		}
>  	}

As above, not sure why this was rewritten, and similar comments as
before apply.