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Commit 79fb4ad6 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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x86: Fix the NMI nesting comments 



Some of the comments for the nesting NMI algorithm were stale and
had some references to some prototypes that were first tried.

I also updated the comments to be a little easier to understand
the flow of the code. It definitely needs the documentation.

Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 62610913

arch/x86/kernel/entry_64.S

+8 −6
Original line number Original line Diff line number Diff line
@@ -1624,11 +1624,12 @@ first_nmi: 
	 * | pt_regs                 |

	 * | pt_regs                 |

	 * +-------------------------+

	 * +-------------------------+

	 *

	 *

	 * The saved RIP is used to fix up the copied RIP that a nested

	 * The saved stack frame is used to fix up the copied stack frame

	 * NMI may zero out. The original stack frame and the temp storage

	 * that a nested NMI may change to make the interrupted NMI iret jump

	 * to the repeat_nmi. The original stack frame and the temp storage

	 * is also used by nested NMIs and can not be trusted on exit.

	 * is also used by nested NMIs and can not be trusted on exit.

	 */

	 */

	/* Do not pop rdx, nested NMIs will corrupt it */

	/* Do not pop rdx, nested NMIs will corrupt that part of the stack */

	movq (%rsp), %rdx

	movq (%rsp), %rdx

	CFI_RESTORE rdx

	CFI_RESTORE rdx
@@ -1641,6 +1642,8 @@ first_nmi: 
	.endr

	.endr

	CFI_DEF_CFA_OFFSET SS+8-RIP

	CFI_DEF_CFA_OFFSET SS+8-RIP





	/* Everything up to here is safe from nested NMIs */



	/*

	/*

	 * If there was a nested NMI, the first NMI's iret will return

	 * If there was a nested NMI, the first NMI's iret will return

	 * here. But NMIs are still enabled and we can take another

	 * here. But NMIs are still enabled and we can take another
@@ -1667,9 +1670,8 @@ end_repeat_nmi: 




	/*

	/*

	 * Everything below this point can be preempted by a nested

	 * Everything below this point can be preempted by a nested

	 * NMI if the first NMI took an exception. Repeated NMIs

	 * NMI if the first NMI took an exception and reset our iret stack

	 * caused by an exception and nested NMI will start here, and

	 * so that we repeat another NMI.

	 * can still be preempted by another NMI.

	 */

	 */

	pushq_cfi $-1		/* ORIG_RAX: no syscall to restart */

	pushq_cfi $-1		/* ORIG_RAX: no syscall to restart */

	subq $ORIG_RAX-R15, %rsp

	subq $ORIG_RAX-R15, %rsp