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

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Message-ID: <20230613224545.902376621@linutronix.de>
Date:   Wed, 14 Jun 2023 01:39:46 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     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>
Subject: [patch 17/17] x86/fpu: Move FPU initialization into arch_cpu_finalize_init()

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>
---
 arch/x86/kernel/cpu/common.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1604,8 +1604,6 @@ static void __init early_identify_cpu(st
 
 	sld_setup(c);
 
-	fpu__init_system();
-
 #ifdef CONFIG_X86_32
 	/*
 	 * Regardless of whether PCID is enumerated, the SDM says
@@ -2287,8 +2285,6 @@ void cpu_init(void)
 
 	doublefault_init_cpu_tss();
 
-	fpu__init_cpu();
-
 	if (is_uv_system())
 		uv_cpu_init();
 
@@ -2304,6 +2300,7 @@ void cpu_init_secondary(void)
 	 */
 	cpu_init_exception_handling();
 	cpu_init();
+	fpu__init_cpu();
 }
 #endif
 
@@ -2396,6 +2393,13 @@ void __init arch_cpu_finalize_init(void)
 			'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 	}
 
+	/*
+	 * Must be before alternatives because it might set or clear
+	 * feature bits.
+	 */
+	fpu__init_system();
+	fpu__init_cpu();
+
 	alternative_instructions();
 
 	if (IS_ENABLED(CONFIG_X86_64)) {