Re: intel_pstate_get_hwp_cap on wrong CPU

[srinivas pandruvada <srinivas.pandruvada@linux.intel.com>]

Hi,
On Fri, 2024-05-31 at 13:02 +0200, Sebastian Andrzej Siewior wrote:
> On 2024-05-29 16:08:19 [-0700], srinivas pandruvada wrote:
> > Hi Sebastian,
> Hi,
> 
> > On Wed, 2024-05-29 at 17:57 +0200, Sebastian Andrzej Siewior wrote:
> > > Hi,
> > > 
> > > this just popped up:
> > > > [ 6538.614568] unchecked MSR access error: RDMSR from 0x771 at
> > > > rIP:
> > 
> > Please check if the attached change fixes?
> 
> it should based on the callchain. Let me test it in a few…
> 
> Would you mind letting
>   /sys/devices/system/cpu/intel_pstate/num_pstates
> 
> reporting something sane? Not 4294967285 but 0 for instance? Would
> that
> make sense?
> 
It should be some good value, usually less than 50. Do you see this
high number without even triggering condition, which caused warning?

In your system, firmware changed performance notifying via ACPI. That
method is deprecated for a while. You are using Haswell, which has this
support. But deprecated from Skylake.

> …
> > From f85a83508ef029bceaf9192cb648d66f32b61d02 Mon Sep 17 00:00:00
> > 2001
> > From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> > Date: Wed, 29 May 2024 15:30:49 -0700
> > Subject: [PATCH] cpufreq: intel_pstate: Fix unchecked HWP MSR
> > access
> > 
> > HWP MSR 0x771 can be only read on a CPU which supports HWP and
> > enabled.
> > Hence intel_pstate_get_hwp_cap() can only be called when hwp_active
> > is
> > true.
> > 
> > Reported-by: Sebastian Reichel <sebastian.reichel@collabora.com>
> 
> Did Sebastian _Reichel_ report it, too?
My mistake. I picked up wrong Sebastian. Sorry.

Thanks,
Srinivas

> 
> > Closes:
> > https://lore.kernel.org/linux-pm/20240529155740.Hq2Hw7be@linutronix.de/
> 
> Because this my report ;)
> 
> > Fixes: e8217b4bece3 ("cpufreq: intel_pstate: Update the maximum CPU
> > frequency consistently")
> > Signed-off-by: Srinivas Pandruvada
> > <srinivas.pandruvada@linux.intel.com>
> 
> Sebastian