linux-kernel - [PATCH 4.4 07/24] x86/fpu: Fix no387 regression

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Date:   Thu, 14 Jun 2018 16:05:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Quentin Casasnovas <quentin.casasnovas@...cle.com>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        yu-cheng yu <yu-cheng.yu@...el.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.4 07/24] x86/fpu: Fix no387 regression

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@...nel.org>

commit f363938c70a04e6bc99023a5e0c44ef7879b903f upstream.

After fixing FPU option parsing, we now parse the 'no387' boot option
too early: no387 clears X86_FEATURE_FPU before it's even probed, so
the boot CPU promptly re-enables it.

I suspect it gets even more confused on SMP.

Fix the probing code to leave X86_FEATURE_FPU off if it's been
disabled by setup_clear_cpu_cap().

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: yu-cheng yu <yu-cheng.yu@...el.com>
Fixes: 4f81cbafcce2 ("x86/fpu: Fix early FPU command-line parsing")
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/fpu/init.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -78,13 +78,15 @@ static void fpu__init_system_early_gener
 	cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
 	write_cr0(cr0);

-	asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
-		     : "+m" (fsw), "+m" (fcw));
+	if (!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
+		asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
+			     : "+m" (fsw), "+m" (fcw));

-	if (fsw == 0 && (fcw & 0x103f) == 0x003f)
-		set_cpu_cap(c, X86_FEATURE_FPU);
-	else
-		clear_cpu_cap(c, X86_FEATURE_FPU);
+		if (fsw == 0 && (fcw & 0x103f) == 0x003f)
+			set_cpu_cap(c, X86_FEATURE_FPU);
+		else
+			clear_cpu_cap(c, X86_FEATURE_FPU);
+	}

 #ifndef CONFIG_MATH_EMULATION
 	if (!cpu_has_fpu) {