[PATCH] cpufreq: intel_pstate: Fix unchecked HWP MSR access

[Srinivas Pandruvada]

Fix unchecked MSR access error for processors with no HWP support. On
such processors, maximum frequency can be changed by the system firmware
using ACPI event ACPI_PROCESSOR_NOTIFY_HIGEST_PERF_CHANGED. This results
in accessing HWP MSR 0x771.

Call Trace:
	<TASK>
	generic_exec_single+0x58/0x120
	smp_call_function_single+0xbf/0x110
	rdmsrl_on_cpu+0x46/0x60
	intel_pstate_get_hwp_cap+0x1b/0x70
	intel_pstate_update_limits+0x2a/0x60
	acpi_processor_notify+0xb7/0x140
	acpi_ev_notify_dispatch+0x3b/0x60

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 Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Closes: https://lore.kernel.org/linux-pm/20240529155740.Hq2Hw7be@xxxxxxxxxxxxx/
Fixes: e8217b4bece3 ("cpufreq: intel_pstate: Update the maximum CPU frequency consistently")
Tested-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
---
 drivers/cpufreq/intel_pstate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 4b986c044741..65d3f79104bd 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1153,7 +1153,8 @@ static void intel_pstate_update_policies(void)
 static void __intel_pstate_update_max_freq(struct cpudata *cpudata,
 					   struct cpufreq_policy *policy)
 {
-	intel_pstate_get_hwp_cap(cpudata);
+	if (hwp_active)
+		intel_pstate_get_hwp_cap(cpudata);
 
 	policy->cpuinfo.max_freq = READ_ONCE(global.no_turbo) ?
 			cpudata->pstate.max_freq : cpudata->pstate.turbo_freq;
-- 
2.25.1