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From:   Jinpu Wang <jinpu.wang@profitbricks.com>
Date:   Mon, 20 Aug 2018 10:05:49 +0200
Message-ID: <CAMGffEk=6eVgB=A--FyooDoVPY4mEiOdf=yNnqdX4cF6Ud_NuA@mail.gmail.com>
Subject: Re: [BUG]smt sysfs dir missing on 4.4.148 and 4.14.63
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable <stable@vger.kernel.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@kernel.org>, konrad.wilk@oracle.com
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On Sat, Aug 18, 2018 at 2:50 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Fri, 17 Aug 2018, Greg Kroah-Hartman wrote:
> > On Fri, Aug 17, 2018 at 02:39:00PM +0200, Jinpu Wang wrote:
> > >
> > > 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.
> >
> > So do we need a new configuration dependancy here to resolve this
> > problem?  Why is this not an issue in Linus's tree?
>
> That's probably the same problem on Linus tree. Have not tested it yet
> though. I'll have a look.
>
> Thanks,
>
>         tglx
>
Yeah, it's the same problem on Linus tree.

Probably makes sense to do the following, I can sent a formal patch if
you think it's right thing to do:

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b0312f8..8a52f0b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -188,7 +188,7 @@ config X86
        select HAVE_SYSCALL_TRACEPOINTS
        select HAVE_UNSTABLE_SCHED_CLOCK
        select HAVE_USER_RETURN_NOTIFIER
-       select HOTPLUG_SMT                      if SMP
+       select HOTPLUG_SMT                      if SMP && HOTPLUG_CPU
        select IRQ_FORCED_THREADING
        select NEED_SG_DMA_LENGTH
        select PCI_LOCKLESS_CONFIG


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Jack Wang
Linux Kernel Developer

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