x86/fpu: Fix math emulation in eager fpu mode

commit 4ecd16ec7059390b430af34bd8bc3ca2b5dcef9a upstream.

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 <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.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 84de3d4f675c2bccc01899427e6f79a20a98e6af..146d838e6ee77de66f26615508914e4d64588992 100644 (file)
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -596,7 +596,8 @@ 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 f9734186a57e12b0a55135bc4ca54e5234fb8c81..6aa0b519c8510e476b20427d3f920ee513b6f522 100644 (file)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -437,7 +437,7 @@ void fpu__clear(struct fpu *fpu)
 {
        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__drop(fpu);
        } else {

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 1fbd2631be6062b0f5e38e69719aea3c4b8af810..8c73bf1492b865d64e6a357d8c689cebf88fc66a 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -751,7 +751,6 @@ 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) {