Commit f363938c authored Jan 21, 2016 by Andy Lutomirski Committed by Ingo Molnar Mar 09, 2016

x86/fpu: Fix 'no387' regression



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@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: yu-cheng yu <yu-cheng.yu@intel.com>
Fixes: 4f81cbaf ("x86/fpu: Fix early FPU command-line parsing")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent e2857b8f

arch/x86/kernel/fpu/init.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -78,6 +78,7 @@ static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
		cr0 &= ~(X86_CR0_TS \| X86_CR0_EM);
		write_cr0(cr0);

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

		@@ -85,6 +86,7 @@ static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
		set_cpu_cap(c, X86_FEATURE_FPU);
		else
		clear_cpu_cap(c, X86_FEATURE_FPU);
		}

		#ifndef CONFIG_MATH_EMULATION
		if (!cpu_has_fpu) {