This is a note to let you know that I've just added the patch titled x86/fpu: Fix i486 + no387 boot crash by only saving FPU registers on context switch if there is an FPU to the 4.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-fpu-fix-i486-no387-boot-crash-by-only-saving-fpu-registers-on-context-switch-if-there-is-an-fpu.patch and it can be found in the queue-4.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 2224d616528194b02424c91c2ee254b3d29942c3 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Date: Tue, 16 Oct 2018 22:25:25 +0200 Subject: x86/fpu: Fix i486 + no387 boot crash by only saving FPU registers on context switch if there is an FPU From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> 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 <bigeasy@xxxxxxxxxxxxx> Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Fixes: f1c8cd0176078 ("x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active") Link: http://lkml.kernel.org/r/20181016202525.29437-4-bigeasy@xxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 Patches currently in stable-queue which might be from bigeasy@xxxxxxxxxxxxx are queue-4.18/x86-fpu-fix-i486-no387-boot-crash-by-only-saving-fpu-registers-on-context-switch-if-there-is-an-fpu.patch