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

[Vaibhav Jain <vaibhav@linux.ibm.com>]

Ira Weiny <ira.weiny@intel.com> writes:

> On Wed, Apr 14, 2021 at 09:51:40PM +0530, Vaibhav Jain wrote:
>> Thanks for looking into this patch Ira,
>> 
>> Ira Weiny <ira.weiny@intel.com> 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 <vaibhav@linux.ibm.com>
>> >> ---
>> >>  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.

Will update the warn message in v2.

>
> Ira
>

-- 
Cheers
~ Vaibhav
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