linux-kernel - Re: [Regression] 6.11.0-rc1: AMD CPU boot with error when CPPC feature disabled by BIOS

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

Message-ID: <6cddbf5f.4164.1910710a3b2.Coremail.00107082@163.com>
Date: Wed, 31 Jul 2024 12:33:36 +0800 (CST)
From: "David Wang" <00107082@....com>
To: "Xiaojian Du" <xiaojidu@....com>
Cc: perry.yuan@....com, Alexander.Deucher@....com, Li.Meng@....com, 
	Mario.Limonciello@....com, Xiaojian.Du@....com, Xinmei.Huang@....com, 
	gautham.shenoy@....com, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, rafael.j.wysocki@...el.com, 
	viresh.kumar@...aro.org
Subject: Re: [Regression] 6.11.0-rc1: AMD CPU boot with error when CPPC
 feature disabled by BIOS

At 2024-07-31 12:21:05, "Xiaojian Du" <xiaojidu@....com> wrote:
>
>On 2024/7/31 11:39, David Wang wrote:
>> At 2024-07-31 11:16:14, "Xiaojian Du" <xiaojidu@....com> wrote:
>>> On 2024/7/31 8:25, David Wang wrote:
>>>> Hi Du,
>>>>
>>>> Thanks for the quick response
>>>>
>>>> ...
>>>> I feel that you are arguing for the warning and the errors separately.
>>>> Separately,   I agree warning or error message make sense as you explained,  but together I feel confused:
>>>> Receiving a warning that CPPC feature is disable by BIOS already notify users that amd-pstate would not work, right?
>Warning is not enough, error will guide user to switch to acpi cpu 
>driver or seek more support from OEM.
>>>> Is it possible, that those two condition coexists: CPPC is disabled by BIOS, and  amd-pstate could function properly?
>>>>
>>>>   
>
>No possible, the current amd-pstate driver is based on CPPC feature.
>
>Thanks.
>Xiaojian
>

So, what about the patch I mentioned:  when CPPC is disabled by  BIOS, print warning message and abort amd-pstate driver registration?
(I made a code block mistake in the patch I posted before)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 68c616b572f2..b06faea58fd4 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1837,8 +1837,6 @@ static bool amd_cppc_supported(void)
         * If the CPPC feature is disabled in the BIOS for processors that support MSR-based CPPC,
         * the AMD Pstate driver may not function correctly.
         * Check the CPPC flag and display a warning message if the platform supports CPPC.
-        * Note: below checking code will not abort the driver registeration process because of
-        * the code is added for debugging purposes.
         */
        if (!cpu_feature_enabled(X86_FEATURE_CPPC)) {
                if (cpu_feature_enabled(X86_FEATURE_ZEN1) || cpu_feature_enabled(X86_FEATURE_ZEN2)) {
@@ -1856,6 +1854,7 @@ static bool amd_cppc_supported(void)
-        if (warn)
+        if (warn) {
                pr_warn_once("The CPPC feature is supported but currently disabled by the BIOS.\n"
                                        "Please enable it if your BIOS has the CPPC option.\n");
+               return false;
+         }
        return true;
 } 



Thanks
David