Re: [PATCH] powerpc/hv-gpci: Fix the hcall return value checks in single_gpci_request function

[Akanksha J N <akanksha@linux.ibm.com>]

On 31/01/24 4:56 pm, Kajol Jain wrote:

> Running event hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/
> in one of the system throws below error:
>
>   ---Logs---
>   # perf list | grep hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles
>    hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=?/[Kernel PMU event]
>
>
>   # perf stat -v -e hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ sleep 2
> Using CPUID 00800200
> Control descriptor is not initialized
> Warning:
> hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ event is not supported by the kernel.
> failed to read counter hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/
>
>   Performance counter stats for 'system wide':
>
>     <not supported>      hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/
>
>         2.000700771 seconds time elapsed
>
> The above error is because of the hcall failure as required
> permission "Enable Performance Information Collection" is not set.
> Based on current code, single_gpci_request function did not check the
> error type incase hcall fails and by default returns EINVAL. But we can
> have other reasons for hcall failures like H_AUTHORITY/H_PARAMETER for which
> we need to act accordingly.
> Fix this issue by adding new checks in the single_gpci_request function.
>
> Result after fix patch changes:
>
>   # perf stat -e hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ sleep 2
> Error:
> No permission to enable hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ event.
>
> Fixes: 220a0c609ad1 ("powerpc/perf: Add support for the hv gpci (get performance counter info) interface")
> Reported-by: Akanksha J N <akanksha@linux.ibm.com>
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>

Tested the patch on Power10 system, and the fix works fine.

# ./perf stat -v -e hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=1/ sleep 2
Control descriptor is not initialized
hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=1/: 0 2001246376 2001246376
  Performance counter stats for 'system wide':
                  0      hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=1/
        2.001250313 seconds time elapsed

Tested-by: Akanksha J N <akanksha@linux.ibm.com>

> ---
>   arch/powerpc/perf/hv-gpci.c | 29 +++++++++++++++++++++++++----
>   1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
> index 27f18119fda1..101060facd81 100644
> --- a/arch/powerpc/perf/hv-gpci.c
> +++ b/arch/powerpc/perf/hv-gpci.c
> @@ -695,7 +695,17 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
>   
>   	ret = plpar_hcall_norets(H_GET_PERF_COUNTER_INFO,
>   			virt_to_phys(arg), HGPCI_REQ_BUFFER_SIZE);
> -	if (ret) {
> +
> +	/*
> +	 * ret value as 'H_PARAMETER' corresponds to 'GEN_BUF_TOO_SMALL',
> +	 * which means that the current buffer size cannot accommodate
> +	 * all the information and a partial buffer returned.
> +	 * Since in this function we are only accessing data for a given starting index,
> +	 * we don't need to accommodate whole data and can get required count by
> +	 * accessing very first entry.
> +	 * Hence hcall fails only incase the ret value is other than H_SUCCESS or H_PARAMETER.
> +	 */
> +	if (ret && (ret != H_PARAMETER)) {
>   		pr_devel("hcall failed: 0x%lx\n", ret);
>   		goto out;
>   	}
> @@ -724,7 +734,7 @@ static u64 h_gpci_get_value(struct perf_event *event)
>   					event_get_offset(event),
>   					event_get_length(event),
>   					&count);
> -	if (ret)
> +	if (ret && (ret != H_PARAMETER))
>   		return 0;
>   	return count;
>   }
> @@ -759,6 +769,7 @@ static int h_gpci_event_init(struct perf_event *event)
>   {
>   	u64 count;
>   	u8 length;
> +	unsigned long ret;
>   
>   	/* Not our event */
>   	if (event->attr.type != event->pmu->type)
> @@ -789,13 +800,23 @@ static int h_gpci_event_init(struct perf_event *event)
>   	}
>   
>   	/* check if the request works... */
> -	if (single_gpci_request(event_get_request(event),
> +	ret = single_gpci_request(event_get_request(event),
>   				event_get_starting_index(event),
>   				event_get_secondary_index(event),
>   				event_get_counter_info_version(event),
>   				event_get_offset(event),
>   				length,
> -				&count)) {
> +				&count);
> +
> +	/*
> +	 * ret value as H_AUTHORITY implies that partition is not permitted to retrieve
> +	 * performance information, and required to set
> +	 * "Enable Performance Information Collection" option.
> +	 */
> +	if (ret == H_AUTHORITY)
> +		return -EPERM;
> +
> +	if (ret && (ret != H_PARAMETER)) {
>   		pr_devel("gpci hcall failed\n");
>   		return -EINVAL;
>   	}