linux-kernel - Re: [patch 17/17] x86/fpu: Move FPU initialization into arch_cpu_finalize

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Date:   Fri, 1 Sep 2023 10:30:55 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nikolay Borisov <nik.borisov@...e.com>,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        linux-sh@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        sparclinux@...r.kernel.org, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        linux-um@...ts.infradead.org,
        Richard Henderson <richard.henderson@...aro.org>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Chris Zankel <chris@...kel.net>,
        Tom Lendacky <thomas.lendacky@....com>, semenzato@...gle.com
Subject: Re: [patch 17/17] x86/fpu: Move FPU initialization into
 arch_cpu_finalize_init()

Hi,

On Wed, Jun 14, 2023 at 01:39:46AM +0200, Thomas Gleixner wrote:
> Initializing the FPU during the early boot process is a pointless
> exercise. Early boot is convoluted and fragile enough.
> 
> Nothing requires that the FPU is set up early. It has to be initialized
> before fork_init() because the task_struct size depends on the FPU register
> buffer size.
> 
> Move the initialization to arch_cpu_finalize_init() which is the perfect
> place to do so.
> 
> No functional change.
> 
> This allows to remove quite some of the custom early command line parsing,
> but that's subject to the next installment.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

The backport of this patch into chromeos-5.10 and chromeos-5.15 via stable
relase merges is causing various Chromebooks (not all of them) to crash
early during boot. Subsequent fixes have not addressed the problem for us,
so we already reverted the patch from chromeos-5.15 and will revert it
from chromeos-5.10 as well.

I don't know if this is a Chromebook specific problem, or if it affects
mainline, so this is just a heads-up in case others experience similar
problems.

Thanks,
Guenter