linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced 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]

Date:   Thu, 9 Sep 2021 06:30:23 -0700
From:   Doug Smythies <dsmythies@...us.net>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        dsmythies <dsmythies@...us.net>
Subject: Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced
 by BIOS

On Wed, Sep 8, 2021 at 11:33 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Wed, 2021-09-08 at 20:48 -0700, Doug Smythies wrote:
> > If HWP has been already been enabled by BIOS, it may be
> > necessary to override some kernel command line parameters.
> > Once it has been enabled it requires a reset to be disabled.
> >
> > Signed-off-by: Doug Smythies <dsmythies@...us.net>
> > ---
> >  drivers/cpufreq/intel_pstate.c | 22 ++++++++++++++++------
> >  1 file changed, 16 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index bb4549959b11..073bae5d4498 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -3267,7 +3267,7 @@ static int __init intel_pstate_init(void)
> >                  */
> >                 if ((!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) ||
> >                     intel_pstate_hwp_is_enabled()) {
> > -                       hwp_active++;
> > +                       hwp_active = 1;
> Why this change?

It was just to keep it at 1, but I agree not absolutely needed.

>
> >                         hwp_mode_bdw = id->driver_data;
> >                         intel_pstate.attr = hwp_cpufreq_attrs;
> >                         intel_cpufreq.attr = hwp_cpufreq_attrs;
> > @@ -3347,17 +3347,27 @@ device_initcall(intel_pstate_init);
> >
> >  static int __init intel_pstate_setup(char *str)
> >  {
> > +       /*
> > +        * If BIOS is forcing HWP, then parameter
> > +        * overrides might be needed. Only print
> > +        * the message once, and regardless of
> > +        * any overrides.
> > +        */
> > +       if(!hwp_active
> This part of code is from early_param, Is it possible that
> hwp_active is not 0?

Not at this point, in any testing I did.
But I do not know the authoritative answer
to your question.

>
> > && boot_cpu_has(X86_FEATURE_HWP))
> > +               if(intel_pstate_hwp_is_enabled()){
> > +                       pr_info("HWP enabled by BIOS\n");
> > +                       hwp_active = 1;
> > +               }
> >         if (!str)
> >                 return -EINVAL;
> >
> > -       if (!strcmp(str, "disable"))
> > +       if (!strcmp(str, "disable") && !hwp_active)
> >                 no_load = 1;
> > -       else if (!strcmp(str, "active"))
> > +       if (!strcmp(str, "active"))
> >                 default_driver = &intel_pstate;
> > -       else if (!strcmp(str, "passive"))
> > +       if (!strcmp(str, "passive"))
> >                 default_driver = &intel_cpufreq;
>
> Why "else if" changed to "if" ?

Because it doesn't matter anyway and I would
have had to figure out another qualifier.
This way, and given that this executes once per
intel_pstate command line parameter, the code
executes the way it used to, overall.

>
>
> Thanks,
> Srinivas
>
> > -
> > -       if (!strcmp(str, "no_hwp")) {
> > +       if (!strcmp(str, "no_hwp") && !hwp_active) {
> >                 pr_info("HWP disabled\n");
> >                 no_hwp = 1;
> >         }
>
>