Re: [PATCH v2] powerpc/perf/hv-gpci: bound sysfs output with helpers

[Madhavan Srinivasan <maddy@linux.ibm.com>]

On 4/23/26 9:02 PM, Pengpeng Hou wrote:
> systeminfo_gpci_request() and
> affinity_domain_via_partition_result_parse() hex-encode hypervisor data
> into the single-page sysfs read buffer with sprintf(buf + *n, ...).
> Both helpers only check PAGE_SIZE after the formatting loops have
> already advanced past the end of the buffer.
>
> Add small helpers around sysfs_emit_at() for hex-byte and newline
> appends, and stop once the sysfs buffer is full. This keeps the repeated
> bounds handling local instead of open-coding it at each append site.
>
> Fixes: 71f1c39647d8 ("powerpc/hv_gpci: Add sysfs file inside hv_gpci device to show processor bus topology information")
> Fixes: a15e0d6a6929 ("powerpc/hv_gpci: Add sysfs file inside hv_gpci device to show affinity domain via partition information")
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---
> Changes since v1:
> - refactor the repeated sysfs_emit_at() handling into helpers as suggested
>    by Christophe Leroy
>
> diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
> index 5cac2cf3bd1e..2f543f0671ba 100644
> --- a/arch/powerpc/perf/hv-gpci.c
> +++ b/arch/powerpc/perf/hv-gpci.c
> @@ -11,6 +11,7 @@
>   
>   #include <linux/init.h>
>   #include <linux/perf_event.h>
> +#include <linux/sysfs.h>
>   #include <asm/firmware.h>
>   #include <asm/hvcall.h>
>   #include <asm/io.h>
> @@ -129,11 +130,36 @@ static int sysinfo_counter_request[] = {
>   
>   static DEFINE_PER_CPU(char, hv_gpci_reqb[HGPCI_REQ_BUFFER_SIZE]) __aligned(sizeof(uint64_t));
>   
> +static int hv_gpci_emit_hex_byte(char *buf, size_t *n, u8 byte)
> +{
> +	int len;
> +
> +	len = sysfs_emit_at(buf, *n, "%02x", byte);
> +	if (len <= 0)
> +		return -EFBIG;
> +
> +	*n += len;
> +	return 0;
> +}
> +
> +static int hv_gpci_emit_newline(char *buf, size_t *n)
> +{
> +	int len;
> +
> +	len = sysfs_emit_at(buf, *n, "\n");
> +	if (len <= 0)
> +		return -EFBIG;
> +
> +	*n += len;
> +	return 0;
> +}
> +
>   static unsigned long systeminfo_gpci_request(u32 req, u32 starting_index,
>   			u16 secondary_index, char *buf,
>   			size_t *n, struct hv_gpci_request_buffer *arg)
>   {
>   	unsigned long ret;
> +	int rc;
Concern here is that function return unsignerd long but patch is 
returning int,
so could break the caller.  Better way could be change function prototype to
return int and update all the caller.

Maddy
>   	size_t i, j;
>   
>   	arg->params.counter_request = cpu_to_be32(req);
> @@ -176,9 +202,14 @@ static unsigned long systeminfo_gpci_request(u32 req, u32 starting_index,
>   	for (i = 0; i < be16_to_cpu(arg->params.returned_values); i++) {
>   		j = i * be16_to_cpu(arg->params.cv_element_size);
>   
> -		for (; j < (i + 1) * be16_to_cpu(arg->params.cv_element_size); j++)
> -			*n += sprintf(buf + *n,  "%02x", (u8)arg->bytes[j]);
> -		*n += sprintf(buf + *n,  "\n");
> +		for (; j < (i + 1) * be16_to_cpu(arg->params.cv_element_size); j++) {
> +			rc = hv_gpci_emit_hex_byte(buf, n, (u8)arg->bytes[j]);
> +			if (rc)
> +				return rc;
> +		}
> +		rc = hv_gpci_emit_newline(buf, n);
> +		if (rc)
> +			return rc;
>   	}
>   
>   	if (*n >= PAGE_SIZE) {
> @@ -461,10 +492,14 @@ static ssize_t affinity_domain_via_domain_show(struct device *dev, struct device
>   	return ret;
>   }
>   
> -static void affinity_domain_via_partition_result_parse(int returned_values,
> -			int element_size, char *buf, size_t *last_element,
> -			size_t *n, struct hv_gpci_request_buffer *arg)
> +static int affinity_domain_via_partition_result_parse(int returned_values,
> +						      int element_size,
> +						      char *buf,
> +						      size_t *last_element,
> +						      size_t *n,
> +						      struct hv_gpci_request_buffer *arg)
>   {
> +	int rc;
>   	size_t i = 0, j = 0;
>   	size_t k, l, m;
>   	uint16_t total_affinity_domain_ele, size_of_each_affinity_domain_ele;
> @@ -483,27 +518,40 @@ static void affinity_domain_via_partition_result_parse(int returned_values,
>   	 */
>   	while (i < returned_values) {
>   		k = j;
> -		for (; k < j + element_size; k++)
> -			*n += sprintf(buf + *n,  "%02x", (u8)arg->bytes[k]);
> -		*n += sprintf(buf + *n,  "\n");
> +		for (; k < j + element_size; k++) {
> +			rc = hv_gpci_emit_hex_byte(buf, n, (u8)arg->bytes[k]);
> +			if (rc)
> +				return rc;
> +		}
> +		rc = hv_gpci_emit_newline(buf, n);
> +		if (rc)
> +			return rc;
>   
>   		total_affinity_domain_ele = (u8)arg->bytes[k - 2] << 8 | (u8)arg->bytes[k - 3];
>   		size_of_each_affinity_domain_ele = (u8)arg->bytes[k] << 8 | (u8)arg->bytes[k - 1];
>   
>   		for (l = 0; l < total_affinity_domain_ele; l++) {
>   			for (m = 0; m < size_of_each_affinity_domain_ele; m++) {
> -				*n += sprintf(buf + *n,  "%02x", (u8)arg->bytes[k]);
> +				rc = hv_gpci_emit_hex_byte(buf, n, (u8)arg->bytes[k]);
> +				if (rc)
> +					return rc;
>   				k++;
>   			}
> -			*n += sprintf(buf + *n,  "\n");
> +			rc = hv_gpci_emit_newline(buf, n);
> +			if (rc)
> +				return rc;
>   		}
>   
> -		*n += sprintf(buf + *n,  "\n");
> +		rc = hv_gpci_emit_newline(buf, n);
> +		if (rc)
> +			return rc;
>   		i++;
>   		j = k;
>   	}
>   
>   	*last_element = k;
> +
> +	return 0;
>   }
>   
>   static ssize_t affinity_domain_via_partition_show(struct device *dev, struct device_attribute *attr,
> @@ -514,6 +562,7 @@ static ssize_t affinity_domain_via_partition_show(struct device *dev, struct dev
>   	size_t n = 0;
>   	size_t last_element = 0;
>   	u32 starting_index;
> +	int element_size, rc, returned_values;
>   
>   	arg = (void *)get_cpu_var(hv_gpci_reqb);
>   	memset(arg, 0, HGPCI_REQ_BUFFER_SIZE);
> @@ -546,10 +595,16 @@ static ssize_t affinity_domain_via_partition_show(struct device *dev, struct dev
>   	 * to buffer util we get all the information.
>   	 */
>   	while (ret == H_PARAMETER) {
> -		affinity_domain_via_partition_result_parse(
> -			be16_to_cpu(arg->params.returned_values) - 1,
> -			be16_to_cpu(arg->params.cv_element_size), buf,
> -			&last_element, &n, arg);
> +		returned_values = be16_to_cpu(arg->params.returned_values);
> +		element_size = be16_to_cpu(arg->params.cv_element_size);
> +		rc = affinity_domain_via_partition_result_parse(returned_values - 1,
> +								element_size, buf,
> +								&last_element, &n,
> +								arg);
> +		if (rc) {
> +			put_cpu_var(hv_gpci_reqb);
> +			return rc;
> +		}
>   
>   		if (n >= PAGE_SIZE) {
>   			put_cpu_var(hv_gpci_reqb);
> @@ -578,10 +633,15 @@ static ssize_t affinity_domain_via_partition_show(struct device *dev, struct dev
>   	}
>   
>   parse_result:
> -	affinity_domain_via_partition_result_parse(
> -		be16_to_cpu(arg->params.returned_values),
> -		be16_to_cpu(arg->params.cv_element_size),
> -		buf, &last_element, &n, arg);
> +	returned_values = be16_to_cpu(arg->params.returned_values);
> +	element_size = be16_to_cpu(arg->params.cv_element_size);
> +	rc = affinity_domain_via_partition_result_parse(returned_values,
> +							element_size, buf,
> +							&last_element, &n, arg);
> +	if (rc) {
> +		put_cpu_var(hv_gpci_reqb);
> +		return rc;
> +	}
>   
>   	put_cpu_var(hv_gpci_reqb);
>   	return n;