From 4ecd16ec7059390b430af34bd8bc3ca2b5dcef9a Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sun, 24 Jan 2016 14:38:06 -0800 Subject: [PATCH] x86/fpu: Fix math emulation in eager fpu mode Systems without an FPU are generally old and therefore use lazy FPU switching. Unsurprisingly, math emulation in eager FPU mode is a bit buggy. Fix it. There were two bugs involving kernel code trying to use the FPU registers in eager mode even if they didn't exist and one BUG_ON() that was incorrect. Signed-off-by: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Quentin Casasnovas Cc: Rik van Riel Cc: Sai Praneeth Prakhya Cc: Thomas Gleixner Cc: yu-cheng yu Link: http://lkml.kernel.org/r/b4b8d112436bd6fab866e1b4011131507e8d7fbe.1453675014.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/fpu/internal.h | 3 ++- arch/x86/kernel/fpu/core.c | 2 +- arch/x86/kernel/traps.c | 1 - 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index 0fd440df63f1..a1f78a9fbf41 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -589,7 +589,8 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu) * If the task has used the math, pre-load the FPU on xsave processors * or if the past 5 consecutive context-switches used math. */ - fpu.preload = new_fpu->fpstate_active && + fpu.preload = static_cpu_has(X86_FEATURE_FPU) && + new_fpu->fpstate_active && (use_eager_fpu() || new_fpu->counter > 5); if (old_fpu->fpregs_active) { diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index d25097c3fc1d..08e1e11a05ca 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -423,7 +423,7 @@ void fpu__clear(struct fpu *fpu) { WARN_ON_FPU(fpu != ¤t->thread.fpu); /* Almost certainly an anomaly */ - if (!use_eager_fpu()) { + if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) { /* FPU state will be reallocated lazily at the first use. */ fpu__drop(fpu); } else { diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index ade185a46b1d..87f80febf477 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -750,7 +750,6 @@ dotraplinkage void do_device_not_available(struct pt_regs *regs, long error_code) { RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); - BUG_ON(use_eager_fpu()); #ifdef CONFIG_MATH_EMULATION if (read_cr0() & X86_CR0_EM) { -- 2.45.2