From 1fd466efc88c48f50e5ee29f4dbb4e210a889172 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 8 Dec 2011 12:32:27 -0500 Subject: [PATCH] x86: Document the NMI handler about not using paranoid_exit Linus cleaned up the NMI handler but it still needs some comments to explain why it uses save_paranoid but not paranoid_exit. Just to keep others from adding that in the future, document why it's not used. Cc: Linus Torvalds Cc: Andi Kleen Signed-off-by: Steven Rostedt --- arch/x86/kernel/entry_64.S | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 3819ea9..d1d5434 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1480,9 +1480,16 @@ END(error_exit) ENTRY(nmi) INTR_FRAME PARAVIRT_ADJUST_EXCEPTION_FRAME - pushq_cfi $-1 + pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */ subq $ORIG_RAX-R15, %rsp CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15 + /* + * Use save_paranoid to handle SWAPGS, but no need to use paranoid_exit + * as we should not be calling schedule in NMI context. + * Even with normal interrupts enabled. An NMI should not be + * setting NEED_RESCHED or anything that normal interrupts and + * exceptions might do. + */ call save_paranoid DEFAULT_FRAME 0 /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */ -- 2.7.4