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: 4f81cbafcce2 ("x86/fpu: Fix early FPU command-line parsing")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 6d9f0a7..d53ab3d 100644 (file)
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -78,13 +78,15 @@ static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
        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) {