Commit 4ecd16ec authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

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: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: yu-cheng yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/b4b8d112436bd6fab866e1b4011131507e8d7fbe.1453675014.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 765bdb40
...@@ -589,7 +589,8 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu) ...@@ -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 * If the task has used the math, pre-load the FPU on xsave processors
* or if the past 5 consecutive context-switches used math. * 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); (use_eager_fpu() || new_fpu->counter > 5);
if (old_fpu->fpregs_active) { if (old_fpu->fpregs_active) {
......
...@@ -423,7 +423,7 @@ void fpu__clear(struct fpu *fpu) ...@@ -423,7 +423,7 @@ void fpu__clear(struct fpu *fpu)
{ {
WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */ WARN_ON_FPU(fpu != &current->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 state will be reallocated lazily at the first use. */
fpu__drop(fpu); fpu__drop(fpu);
} else { } else {
......
...@@ -750,7 +750,6 @@ dotraplinkage void ...@@ -750,7 +750,6 @@ dotraplinkage void
do_device_not_available(struct pt_regs *regs, long error_code) do_device_not_available(struct pt_regs *regs, long error_code)
{ {
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
BUG_ON(use_eager_fpu());
#ifdef CONFIG_MATH_EMULATION #ifdef CONFIG_MATH_EMULATION
if (read_cr0() & X86_CR0_EM) { if (read_cr0() & X86_CR0_EM) {
......
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