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

Ira Weiny [off-list ref] writes:

On Wed, Apr 14, 2021 at 09:51:40PM +0530, Vaibhav Jain wrote:

quoted

Thanks for looking into this patch Ira,

Ira Weiny [off-list ref] writes:

quoted

On Wed, Apr 14, 2021 at 06:10:26PM +0530, Vaibhav Jain wrote:

quoted

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 <redacted>
---
 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