linux-kernel - Re: [patch 02/38] x86/cpu: Use native_wrmsrl() in load_percpu

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Date:   Sun, 17 Jul 2022 22:13:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andrew Cooper <Andrew.Cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch 02/38] x86/cpu: Use native_wrmsrl() in
 load_percpu_segment()

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.