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

[Ira Weiny <ira.weiny@intel.com>]

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'?

Ira
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