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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andrew Cooper <Andrew.Cooper3@citrix.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     "x86@kernel.org" <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Johannes Wikner <kwikner@ethz.ch>,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
        Joao Moreira <joao.moreira@intel.com>,
        Joseph Nuzman <joseph.nuzman@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [patch 02/38] x86/cpu: Use native_wrmsrl() in
 load_percpu_segment()
In-Reply-To: <87tu7fwlhr.ffs@tglx>
References: <20220716230344.239749011@linutronix.de>
 <20220716230952.787452088@linutronix.de>
 <0bec8fe2-d1e3-f01c-6e52-06ab542efdd8@citrix.com> <87zgh7wo91.ffs@tglx>
 <87tu7fwlhr.ffs@tglx>
Date:   Sun, 17 Jul 2022 22:13:10 +0200
Message-ID: <87r12jwl9l.ffs@tglx>
MIME-Version: 1.0
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On Sun, Jul 17 2022 at 22:08, Thomas Gleixner wrote:
> On Sun, Jul 17 2022 at 21:08, Thomas Gleixner wrote:
> loadsegment_simple() was a red herring. The gs segment is already zero.
>
> So what explodes here is the early boot when switching from early per
> CPU to the real per CPU area.
>
> start_kernel()
>         .....
>         setup_per_cpu_areas();
>         smp_prepare_boot_cpu()

Bah. switch_to_new_gdt() is already invoked from setup_per_cpu_areas()
and then again in smp_prepare_boot_cpu() and once more in cpu_init(),

What a mess.