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Subject[PATCH 6/8] x86/fpu: #NM without FPU emulation is an error
Date
don't use CR0.TS.  Make it an error rather than making nonsensical
changes to the FPU state.

(The cond_local_irq_enable() appears to have been pointless, too.)

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/kernel/traps.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bd4e3d4d3625..bf0c6d049080 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -853,6 +853,8 @@ do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
dotraplinkage void
do_device_not_available(struct pt_regs *regs, long error_code)
{
+ unsigned long cr0;
+
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");

#ifdef CONFIG_MATH_EMULATION
@@ -866,10 +868,20 @@ do_device_not_available(struct pt_regs *regs, long error_code)
return;
}
#endif
- fpu__restore(&current->thread.fpu); /* interrupts still off */
-#ifdef CONFIG_X86_32
- cond_local_irq_enable(regs);
-#endif
+
+ /* This should not happen. */
+ cr0 = read_cr0();
+ if (WARN(cr0 & X86_CR0_TS, "CR0.TS was set")) {
+ /* Try to fix it up and carry on. */
+ write_cr0(cr0 & ~X86_CR0_TS);
+ } else {
+ /*
+ * Something terrible happened, and we're better off trying
+ * to kill the task than getting stuck in a never-ending
+ * loop of #NM faults.
+ */
+ die("unexpected #NM exception", regs, error_code);
+ }
}
NOKPROBE_SYMBOL(do_device_not_available);

--
2.7.4
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