x86: Allow nesting of the debug stack IDT setting

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / cpu / common.c

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 82f29e70d05833b7b3b6e0b7789a46ef9a75c4b8..6b9333b429ba1910637bf29c63bbe0712064022e 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1101,14 +1101,20 @@ int is_debug_stack(unsigned long addr)
                 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
 }
 
+static DEFINE_PER_CPU(u32, debug_stack_use_ctr);
+
 void debug_stack_set_zero(void)
 {
+       this_cpu_inc(debug_stack_use_ctr);
        load_idt((const struct desc_ptr *)&nmi_idt_descr);
 }
 
 void debug_stack_reset(void)
 {
-       load_idt((const struct desc_ptr *)&idt_descr);
+       if (WARN_ON(!this_cpu_read(debug_stack_use_ctr)))
+               return;
+       if (this_cpu_dec_return(debug_stack_use_ctr) == 0)
+               load_idt((const struct desc_ptr *)&idt_descr);
 }
 
 #else  /* CONFIG_X86_64 */