Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull straggler x86 fixes from Peter Anvin:
 "Three groups of patches:

  - EFI boot stub documentation and the ability to print error messages;
  - Removal for PTRACE_ARCH_PRCTL for x32 (obsolete interface which
    should never have been ported, and the port is broken and
    potentially dangerous.)
  - ftrace stack corruption fixes.  I'm not super-happy about the
    technical implementation, but it is probably the least invasive in
    the short term.  In the future I would like a single method for
    nesting the debug stack, however."

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, x32, ptrace: Remove PTRACE_ARCH_PRCTL for x32
  x86, efi: Add EFI boot stub documentation
  x86, efi; Add EFI boot stub console support
  x86, efi: Only close open files in error path
  ftrace/x86: Do not change stacks in DEBUG when calling lockdep
  x86: Allow nesting of the debug stack IDT setting
  x86: Reset the debug_stack update counter
  ftrace: Use breakpoint method to update ftrace caller
  ftrace: Synchronize variable setting with breakpoints

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 82f29e70d05..6b9333b429b 100644
--- 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 */