linux-kernel - Re: [BUG]smt sysfs dir missing on 4.4.148 and 4.14.63

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Date:   Mon, 20 Aug 2018 15:20:33 +0200
From:   Jinpu Wang <jinpu.wang@...fitbricks.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable <stable@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>, konrad.wilk@...cle.com,
        Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [BUG]smt sysfs dir missing on 4.4.148 and 4.14.63

On Mon, Aug 20, 2018 at 3:02 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Mon, 20 Aug 2018, Jinpu Wang wrote:
>
> > On Sat, Aug 18, 2018 at 2:50 PM Thomas Gleixner <tglx@...utronix.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=full' probably also other combination.
> > > > >
> > > > > With CONFIG_HOTPLUG_CPU=y, 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
>
> That works, but we might as well force 'select HOTPLUG_CPU if SMP' so the
> L1TF mitigations are functional. Sigh....
>
> Thanks,
>
>         tglx
right, sth like?
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b0312f8..5852948 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -188,7 +188,8 @@ config X86
        select HAVE_SYSCALL_TRACEPOINTS
        select HAVE_UNSTABLE_SCHED_CLOCK
        select HAVE_USER_RETURN_NOTIFIER
-       select HOTPLUG_SMT                      if SMP
+       select HOTPLUG_CPU                      if SMP
+       select HOTPLUG_SMT                      if SMP && HOTPLUG_CPU
        select IRQ_FORCED_THREADING
        select NEED_SG_DMA_LENGTH
        select PCI_LOCKLESS_CONFIG



-- 
Thanks,

Jack Wang
Linux Kernel Developer

ProfitBricks GmbH
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D - 10405 Berlin

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