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Subject[PATCH 8/24] i386: convert hardware exception 7 to an interrupt gate
Date
From: Alexander van Heukelum <heukelum@fastmail.fm>

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>
---
arch/x86/kernel/entry_32.S | 15 ++-------------
arch/x86/kernel/traps_32.c | 14 +++++++++++++-
2 files changed, 15 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 109792b..5a88585 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 5d8d057..3ddd71b 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>
@@ -1234,6 +1235,17 @@ 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;
@@ -1253,7 +1265,7 @@ 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);
--
1.5.4.3


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