Re: [PATCH] powerpc/perf/hv-gpci: bound sysfs formatting with sysfs_emit_at()

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 17/04/2026 à 09:48, Pengpeng Hou a écrit :
> 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.
> 
> Switch these appends to sysfs_emit_at() and stop once the sysfs buffer is
> full.

You are changing several time a single lines by multiples lines that 
look pretty similar. Can you refactor in a helper function ?

> 
> 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")
> Cc: stable@vger.kernel.org
> 
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---
>   arch/powerpc/perf/hv-gpci.c | 56 +++++++++++++++++++++++++++++++------
>   1 file changed, 47 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
> index 5cac2cf3bd1e..325b80f01629 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>
> @@ -134,6 +135,7 @@ static unsigned long systeminfo_gpci_request(u32 req, u32 starting_index,
>   			size_t *n, struct hv_gpci_request_buffer *arg)
>   {
>   	unsigned long ret;
> +	int len;
>   	size_t i, j;
>   
>   	arg->params.counter_request = cpu_to_be32(req);
> @@ -176,9 +178,17 @@ 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++) {
> +			len = sysfs_emit_at(buf, *n, "%02x", (u8)arg->bytes[j]);
> +			if (!len)
> +				return -EFBIG;
> +			*n += len;
> +		}
> +		len = sysfs_emit_at(buf, *n, "\n");
> +		if (!len)
> +			return -EFBIG;
> +		*n += len;
>   	}
>   
>   	if (*n >= PAGE_SIZE) {
> @@ -465,6 +475,7 @@ 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)
>   {
> +	int len;
>   	size_t i = 0, j = 0;
>   	size_t k, l, m;
>   	uint16_t total_affinity_domain_ele, size_of_each_affinity_domain_ele;
> @@ -483,22 +494,49 @@ 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++) {
> +			len = sysfs_emit_at(buf, *n, "%02x", (u8)arg->bytes[k]);
> +			if (!len) {
> +				*n = PAGE_SIZE;
> +				return;
> +			}
> +			*n += len;
> +		}
> +		len = sysfs_emit_at(buf, *n, "\n");
> +		if (!len) {
> +			*n = PAGE_SIZE;
> +			return;
> +		}
> +		*n += len;
>   
>   		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]);
> +				len = sysfs_emit_at(buf, *n, "%02x",
> +						    (u8)arg->bytes[k]);
> +				if (!len) {
> +					*n = PAGE_SIZE;
> +					return;
> +				}
> +				*n += len;
>   				k++;
>   			}
> -			*n += sprintf(buf + *n,  "\n");
> +			len = sysfs_emit_at(buf, *n, "\n");
> +			if (!len) {
> +				*n = PAGE_SIZE;
> +				return;
> +			}
> +			*n += len;
>   		}
>   
> -		*n += sprintf(buf + *n,  "\n");
> +		len = sysfs_emit_at(buf, *n, "\n");
> +		if (!len) {
> +			*n = PAGE_SIZE;
> +			return;
> +		}
> +		*n += len;
>   		i++;
>   		j = k;
>   	}