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

From: Dan Williams <dan.j.williams@intel.com>
To: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] powerpc/papr_scm: Reduce error severity if nvdimm stats inaccessible
Date: Thu, 15 Apr 2021 10:03:01 -0700	[thread overview]
Message-ID: <CAPcyv4g=YqcOxwS5Q=_Z=fx5WCwU1t0M3me5OFeQodckKSfm9A@mail.gmail.com> (raw)
In-Reply-To: <87k0p3lqmq.fsf@vajain21.in.ibm.com>

On Thu, Apr 15, 2021 at 4:44 AM Vaibhav Jain <vaibhav@linux.ibm.com> wrote:
>
> Thanks for looking into this Dan,
>
> Dan Williams <dan.j.williams@intel.com> writes:
>
> > On Wed, Apr 14, 2021 at 5:40 AM Vaibhav Jain <vaibhav@linux.ibm.com> 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;
> >
> > So userspace can spam the kernel log? Why is kernel log message needed
> > at all? EPERM told the caller what happened.
> Currently this error message is only reported during probe of the
> nvdimm. So userspace cannot directly spam kernel log.

Oh, ok, I saw things like papr_pdsm_fuel_gauge() in the call stack and
thought this was reachable through an ioctl. Sorry for the noise.
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