4.18-stable review patch. If anyone has any objections, please let me know.
------------------ From: Sebastian Andrzej Siewior <[email protected]> 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 <[email protected]> Reviewed-by: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Fixes: f1c8cd0176078 ("x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active") Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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
