4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sebastian Andrzej Siewior <bige...@linutronix.de>
commit 2224d616528194b02424c91c2ee254b3d29942c3 upstream.
Booting an i486 with "no387 nofxsr" ends with with the following crash:
math_emulate: 0060:c101987d
Kernel panic - not syncing: Math emulation needed in kernel
on the first context switch in user land.
The reason is that copy_fpregs_to_fpstate() tries FNSAVE which does not work
as the FPU is turned off.
This bug was introduced in:
f1c8cd0176078 ("x86/fpu: Change fpu->fpregs_active users to
fpu->fpstate_active")
Add a check for X86_FEATURE_FPU before trying to save FPU registers (we
have such a check in switch_fpu_finish() already).
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Reviewed-by: Andy Lutomirski <l...@kernel.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: sta...@vger.kernel.org
Fixes: f1c8cd0176078 ("x86/fpu: Change fpu->fpregs_active users to
fpu->fpstate_active")
Link: http://lkml.kernel.org/r/20181016202525.29437-4-bige...@linutronix.de
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
arch/x86/include/asm/fpu/internal.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -528,7 +528,7 @@ static inline void fpregs_activate(struc
static inline void
switch_fpu_prepare(struct fpu *old_fpu, int cpu)
{
- if (old_fpu->initialized) {
+ if (static_cpu_has(X86_FEATURE_FPU) && old_fpu->initialized) {
if (!copy_fpregs_to_fpstate(old_fpu))
old_fpu->last_cpu = -1;
else
