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Date: Mon, 27 Nov 2017 18:32:46 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "H . Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 10/24] x86/mm/kaiser: Map the entry stack variables
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References: <20171127104923.14378-1-mingo@kernel.org> <20171127104923.14378-11-mingo@kernel.org> <20171127172927.ng5iigkvnkfgmixb@hirez.programming.kicks-ass.net>
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On Mon, 27 Nov 2017, Peter Zijlstra wrote:

> On Mon, Nov 27, 2017 at 11:49:09AM +0100, Ingo Molnar wrote:
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index 7b348cc33e2d..f4f4ab8525bd 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -1515,7 +1515,7 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count);
> >   * the top of the kernel stack.  Use an extra percpu variable to track the
> >   * top of the kernel stack directly.
> >   */
> > -DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) =
> > +DEFINE_PER_CPU_USER_MAPPED(unsigned long, cpu_current_top_of_stack) =
> >  	(unsigned long)&init_thread_union + THREAD_SIZE;
> >  EXPORT_PER_CPU_SYMBOL(cpu_current_top_of_stack);
> 
> I can't find where we would access this one without already having
> switched to kernel CR3.
> 
> A kernel with this entire patch reverted seems to boot for me.

Yes, it's not longer required.