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Sender: Guenter Roeck <groeck7@gmail.com>
Date:   Fri, 1 Sep 2023 14:09:17 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Nikolay Borisov <nik.borisov@suse.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Ahmed S. Darwish" <darwi@linutronix.de>,
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        Russell King <linux@armlinux.org.uk>,
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        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
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Subject: Re: [patch 17/17] x86/fpu: Move FPU initialization into
 arch_cpu_finalize_init()
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On Fri, Sep 01, 2023 at 09:02:19PM +0300, Nikolay Borisov wrote:
> 
> 
> 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.

I understand, but that is still better than not being able to boot
in the first place.

Thanks,
Guenter