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From:   Jinpu Wang <jinpu.wang@profitbricks.com>
Date:   Fri, 17 Aug 2018 14:39:00 +0200
Message-ID: <CAMGffEnKt0xcc6LhNdZQGRmckJ3qCFxCOnQ3owZmWWiaKYdYuw@mail.gmail.com>
Subject: Re: [BUG]smt sysfs dir missing on 4.4.148 and 4.14.63
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        stable <stable@vger.kernel.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@kernel.org>, konrad.wilk@oracle.com
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On Thu, Aug 16, 2018 at 6:48 PM Jinpu Wang <jinpu.wang@profitbricks.com> wr=
ote:
>
> On Thu, Aug 16, 2018 at 6:39 PM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Thu, Aug 16, 2018 at 06:28:59PM +0200, Jinpu Wang wrote:
> > > On Thu, Aug 16, 2018 at 5:51 PM Greg Kroah-Hartman
> > > <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Thu, Aug 16, 2018 at 05:43:23PM +0200, Jinpu Wang wrote:
> > > > > Hi Greg, hi Thomas,
> > > > >
> > > > > I noticed /sys/devices/system/cpu/smt dir is missing on 4.4.148 a=
nd
> > > > > 4.14.63, default setting.
> > > >
> > > > For 4.4, I would be amazed if anything was there, the backport was =
done
> > > > only to handle the local user issue, not the "full" protection.  So
> > > > please try 4.9 or 4.14.
> > > Thanks for quick reply. Right, just checked. the patch for create the
> > > sysfs entry is missing.
> >
> > What patch is that?  What is the git commit id that we missed?
> >
> > > > How about 4.17 and 4.18, do those trees work properly for you?
> > > I guess it's the same.
> > > >
> > > > > Tried stable/master branch 31130a16d459 ("Merge tag
> > > > > 'for-linus-4.19-rc1-tag' of
> > > > > git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip")
> > > > > It's the same there.
> > > >
> > > > Ah, so we are bug compatible, good :)
> > > I will try test stable master a bit more to gather the full log.
> > > >
> > > > > When boot with 'nosmt' kernel paramter kernel 4.14.63 panic durin=
g
> > > > > boot, 4.4.148 boot fine.
> > > > > The call trace seem irq related, is it known bug?
> > > >
> > > > You are not giving us much to go on here sorry.  We need full detai=
ls,
> > > > and also please cc: lkml and the other developers who worked on thi=
s.
> > > > THomas is on vacation this week.
> > > Now, add more developers to cc, also lkml.
> > >
> > > I have the config and boot dmesg attached for default setting.
> >
> > I see no error in your boot log, what exactly are you worried about?
> 2 problems here:
> 1 According to https://www.kernel.org/doc/html/latest/admin-guide/l1tf.ht=
ml
>   I expect /sys/devices/system/cpu/smt/, but it's not.
> 2 kernel 4.14.63 panic when I boot with 'nosmt' or 'l1tf=3Dfull', I
> attached the picture here again,
>   I will try to get the full log tomorrow, also test with linus tree.
> >
> > confused,
> >
> > greg k-h
>
> Thanks
I found the problem, CONFIG_HOTPLUG_SMT is enable due to CONFIG_SMP,
but I did explicitly enable CONFIG_HOTPLUG_CPU.

That's why the smt dir is missing, and kernel panic when I boot with
'nosmt' or 'l1tf=3Dfull' probably also other combination.

With CONFIG_HOTPLUG_CPU=3Dy, it works fine so far.

Thanks,
--=20
Jack Wang
Linux Kernel Developer

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