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Date:   Fri, 1 Sep 2023 21:02:19 +0300
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Subject: Re: [patch 17/17] x86/fpu: Move FPU initialization into
 arch_cpu_finalize_init()
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To:     Guenter Roeck <linux@roeck-us.net>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Ahmed S. Darwish" <darwi@linutronix.de>,
        Arnd Bergmann <arnd@arndb.de>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>, loongarch@lists.linux.dev,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-m68k@lists.linux-m68k.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-mips@vger.kernel.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        linux-sh@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        sparclinux@vger.kernel.org, Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-um@lists.infradead.org,
        Richard Henderson <richard.henderson@linaro.org>,
        "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Chris Zankel <chris@zankel.net>,
        Tom Lendacky <thomas.lendacky@amd.com>, semenzato@google.com
References: <20230613223827.532680283@linutronix.de>
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From:   Nikolay Borisov <nik.borisov@suse.com>
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On 1.09.23 г. 20:30 ч., Guenter Roeck wrote:
> 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@linutronix.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.


Another thing - if you choose to revert the arch_finalize patch then 
bear in mind that the GDS' 'force' option is rendered inoperable as the 
FPU can't be disabled due to the way things are sequenced.
> 
> Thanks,
> Guenter