i386: convert hardware exception 7 to an interrupt gate

Handle no coprocessor exception with interrupt initially off.

device_not_available in entry_32.S calls either math_state_restore
or math_emulate. This patch adds an extra indirection to be
able to re-enable interrupts explicitly in traps_32.c

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 15 insertions, 14 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 109792bc7cfa..5a885855fc88 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -760,20 +760,9 @@ ENTRY(device_not_available)
         RING0_INT_FRAME
         pushl $-1                       # mark this as an int
         CFI_ADJUST_CFA_OFFSET 4
-        SAVE_ALL
-        GET_CR0_INTO_EAX
-        testl $0x4, %eax                # EM (math emulation bit)
-        jne device_not_available_emulate
-        preempt_stop(CLBR_ANY)
-        call math_state_restore
-        jmp ret_from_exception
-device_not_available_emulate:
-        pushl $0                        # temporary storage for ORIG_EIP
+        pushl $do_device_not_available
         CFI_ADJUST_CFA_OFFSET 4
-        call math_emulate
-        addl $4, %esp
-        CFI_ADJUST_CFA_OFFSET -4
-        jmp ret_from_exception
+        jmp error_code
         CFI_ENDPROC
 END(device_not_available)
 
diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index 39a6101a6123..5b15f75d0591 100644
--- a/arch/x86/kernel/traps_32.c
+++ b/arch/x86/kernel/traps_32.c
@@ -46,6 +46,7 @@
 #include <linux/edac.h>
 #endif
 
+#include <asm/processor-flags.h>
 #include <asm/arch_hooks.h>
 #include <asm/stacktrace.h>
 #include <asm/processor.h>
@@ -1236,6 +1237,17 @@ asmlinkage void math_emulate(long arg)
 
 #endif /* CONFIG_MATH_EMULATION */
 
+void __kprobes do_device_not_available(struct pt_regs *regs, long error)
+{
+        if (read_cr0() & X86_CR0_EM) {
+                conditional_sti(regs);
+                math_emulate(0);
+        } else {
+                math_state_restore(); /* interrupts still off */
+                conditional_sti(regs);
+        }
+}
+
 void __init trap_init(void)
 {
         int i;
@@ -1255,7 +1267,7 @@ void __init trap_init(void)
         set_system_intr_gate(4, &overflow); /* int4 can be called from all */
         set_intr_gate(5, &bounds);
         set_intr_gate(6, &invalid_op);
-        set_trap_gate(7, &device_not_available);
+        set_intr_gate(7, &device_not_available);
         set_task_gate(8, GDT_ENTRY_DOUBLEFAULT_TSS);
         set_trap_gate(9, &coprocessor_segment_overrun);
         set_trap_gate(10, &invalid_TSS);