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x86/fpu: Fix CPUID-less FPU detection

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The old code didn't work at all because it adjusted the current caps
instead of the forced caps.  Anything it did would be undone later
during CPU identification.  Fix that and, while we're at it, improve
the logging and don't bother running it if CPUID is available.

Reported-by: Matthew Whitehead <tedheadster@gmail.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.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: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/f1134e30cafa73c4e2e68119e9741793622cfd15.1484705016.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-01-18 11:15:41 -08:00 committed by Ingo Molnar
parent 9170fb4094
commit 37ac78b67b
1 changed files with 14 additions and 13 deletions
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27
arch/x86/kernel/fpu/init.c
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@ -48,13 +48,7 @@ void fpu__init_cpu(void)
fpu__init_cpu_xstate();
}
/*
* The earliest FPU detection code.
*
* Set the X86_FEATURE_FPU CPU-capability bit based on
* trying to execute an actual sequence of FPU instructions:
*/
static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
static bool fpu__probe_without_cpuid(void)
{
unsigned long cr0;
u16 fsw, fcw;
@ -65,14 +59,21 @@ 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));
asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
if (fsw == 0 && (fcw & 0x103f) == 0x003f)
set_cpu_cap(c, X86_FEATURE_FPU);
pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
return fsw == 0 && (fcw & 0x103f) == 0x003f;
}
static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
{
if (!boot_cpu_has(X86_FEATURE_CPUID) &&
!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
if (fpu__probe_without_cpuid())
setup_force_cpu_cap(X86_FEATURE_FPU);
else
clear_cpu_cap(c, X86_FEATURE_FPU);
setup_clear_cpu_cap(X86_FEATURE_FPU);
}
#ifndef CONFIG_MATH_EMULATION