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Date:   Fri, 29 Oct 2021 22:29:25 +0200 (CEST)
From:   Julia Lawall <julia.lawall@inria.fr>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
cc:     Doug Smythies <dsmythies@telus.net>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Len Brown <lenb@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: problem in changing from active to passive mode
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On Fri, 29 Oct 2021, Rafael J. Wysocki wrote:

> On Thu, Oct 28, 2021 at 10:18 PM Julia Lawall <julia.lawall@inria.fr> wrote:
> >
> >
> >
> > On Thu, 28 Oct 2021, Rafael J. Wysocki wrote:
> >
> > > On Thu, Oct 28, 2021 at 9:25 PM Julia Lawall <julia.lawall@inria.fr> wrote:
>
> [cut]
>
> > > Attached is a patch to do that, but please note that the 5.9 will need
> > > to be patched too to address this issue.
> >
> > I'm not completely clear on what the new patch is doing and how I should
> > test it.  If I stay in 5.15, the original patch worked for clearing des
> > when going from passive to active.
>
> Sorry for the confusion.
>
> If applied to 5.15-rc alone, the last patch would cause des to be
> cleared when switching from passive to active and if applied to both
> 5.15-rc and 5.9, it would fix the kexec issue as well.
>
> Never mind, though.
>
> The patch attached to this message should cause des to be cleared when
> switching from passive to active (because it is based on the previous
> patch doing that) and it should prevent nonzero des from being leaked
> via the HWP_REQUEST MSR to the new kernel started via kexec.  With
> this patch applied to 5.15-rc des should be 0 when switching from
> passive to active and it should also be 0 after starting another
> kernel via kexec while intel_pstate is running in the passive mode.
>
> Can you please verify that it works as expected?

I booted 5.15 rc6 in active then changed to passive making the des field
non zero, and then changed back to active, making it 0 again.  I them
changed again to passive and kexeced 5.9.  The des field was again 0.

So it looks fine.

thanks,
julia