linux-kernel - [PATCH] cpufreq: intel_pstate: Reporting reasons why driver prematurely exit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-Id: <20190208115658.723-1-e.velu@criteo.com>
Date:   Fri,  8 Feb 2019 12:56:58 +0100
From:   Erwan Velu <erwanaliasr1@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     e.velu@...teo.com,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-pm@...r.kernel.org (open list:INTEL PSTATE DRIVER),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] cpufreq: intel_pstate: Reporting reasons why driver prematurely exit

The init code path have several execeptions where the module can decide not to load.
As CONFIG_X86_INTEL_PSTATE is generally set to Y, the return code is not reachable.
The initialisation code is neither verbose of the reason why it did choose to prematurely exit.

This situation leads to situation where its difficult for a user to determine,
on a given platform, why the driver didn't loaded properly.

This patch is about reporting to the user the reason/context why the driver failed to load.
That is a precious hint when debugging a platform.

Signed-off-by: Erwan Velu <e.velu@...teo.com>
---
 drivers/cpufreq/intel_pstate.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index dd66decf2087..635049095dde 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -2592,8 +2592,10 @@ static int __init intel_pstate_init(void)
 	const struct x86_cpu_id *id;
 	int rc;
 
-	if (no_load)
+	if (no_load) {
+		pr_info("disabling as per user-request\n");
 		return -ENODEV;
+	}
 
 	id = x86_match_cpu(hwp_support_ids);
 	if (id) {
@@ -2606,31 +2608,41 @@ static int __init intel_pstate_init(void)
 		}
 	} else {
 		id = x86_match_cpu(intel_pstate_cpu_ids);
-		if (!id)
+		if (!id) {
+			pr_warn("CPU doesn't support P-states\n");
 			return -ENODEV;
+		}
 
 		copy_cpu_funcs((struct pstate_funcs *)id->driver_data);
 	}
 
-	if (intel_pstate_msrs_not_valid())
+	if (intel_pstate_msrs_not_valid()) {
+		pr_warn("Cannot enable driver as per invalid MSRs\n");
 		return -ENODEV;
+	}
 
 hwp_cpu_matched:
 	/*
 	 * The Intel pstate driver will be ignored if the platform
 	 * firmware has its own power management modes.
 	 */
-	if (intel_pstate_platform_pwr_mgmt_exists())
+	if (intel_pstate_platform_pwr_mgmt_exists()) {
+		pr_warn("Platform already taking care of power management\n");
 		return -ENODEV;
+	}
 
-	if (!hwp_active && hwp_only)
+	if (!hwp_active && hwp_only) {
+		pr_warn("HWP not present\n");
 		return -ENOTSUPP;
+	}
 
 	pr_info("Intel P-state driver initializing\n");
 
 	all_cpu_data = vzalloc(array_size(sizeof(void *), num_possible_cpus()));
-	if (!all_cpu_data)
+	if (!all_cpu_data) {
+		pr_warn("Cannot allocate memory\n");
 		return -ENOMEM;
+	}
 
 	intel_pstate_request_control_from_smm();
 
-- 
2.20.1