Re: [PATCH] powerpc/papr_scm: Reduce error severity if nvdimm stats inaccessible

On 4/15/21 5:18 PM, Vaibhav Jain wrote:
> Ira Weiny <[email protected]> writes:
> 
>> On Wed, Apr 14, 2021 at 09:51:40PM +0530, Vaibhav Jain wrote:
>>> Thanks for looking into this patch Ira,
>>>
>>> Ira Weiny <[email protected]> writes:
>>>
>>>> On Wed, Apr 14, 2021 at 06:10:26PM +0530, Vaibhav Jain wrote:
>>>>> Currently drc_pmem_qeury_stats() generates a dev_err in case
>>>>> "Enable Performance Information Collection" feature is disabled from
>>>>> HMC. The error is of the form below:
>>>>>
>>>>> papr_scm ibm,persistent-memory:ibm,pmemory@44104001: Failed to query
>>>>> 	 performance stats, Err:-10
>>>>>
>>>>> This error message confuses users as it implies a possible problem
>>>>> with the nvdimm even though its due to a disabled feature.
>>>>>
>>>>> So we fix this by explicitly handling the H_AUTHORITY error from the
>>>>> H_SCM_PERFORMANCE_STATS hcall and generating a warning instead of an
>>>>> error, saying that "Performance stats in-accessible".
>>>>>
>>>>> Fixes: 2d02bf835e57('powerpc/papr_scm: Fetch nvdimm performance stats from PHYP')
>>>>> Signed-off-by: Vaibhav Jain <[email protected]>
>>>>> ---
>>>>>  arch/powerpc/platforms/pseries/papr_scm.c | 3 +++
>>>>>  1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>>>>> index 835163f54244..9216424f8be3 100644
>>>>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>>>>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>>>>> @@ -277,6 +277,9 @@ static ssize_t drc_pmem_query_stats(struct papr_scm_priv *p,
>>>>>  		dev_err(&p->pdev->dev,
>>>>>  			"Unknown performance stats, Err:0x%016lX\n", ret[0]);
>>>>>  		return -ENOENT;
>>>>> +	} else if (rc == H_AUTHORITY) {
>>>>> +		dev_warn(&p->pdev->dev, "Performance stats in-accessible");
>>>>> +		return -EPERM;
>>>>
>>>> Is this because of a disabled feature or because of permissions?
>>>
>>> Its because of a disabled feature that revokes permission for a guest to
>>> retrieve performance statistics.
>>>
>>> The feature is called "Enable Performance Information Collection" and
>>> once disabled the hcall H_SCM_PERFORMANCE_STATS returns an error
>>> H_AUTHORITY indicating that the guest doesn't have permission to retrieve
>>> performance statistics.
>>
>> In that case would it be appropriate to have the error message indicate a
>> permission issue?
>>
>> Something like 'permission denied'?
> 
> Yes, Something like "Permission denied while accessing performance
> stats" might be more clear and intuitive.

Hi Vaibhav,
   Thanks for the patch. I agree with Ira and above warning message with "Permission denied" looks more clear.
With that change, patch looks good to me.

Reviewed-By: Kajol Jain<[email protected]>

Thanks,
Kajol Jain
> 
> Will update the warn message in v2.
> 
>>
>> Ira
>>
> 
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