linux-kernel - Re: Perhaps a side effect regarding NMI returns

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Date:	Wed, 07 Dec 2011 11:36:40 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>
Subject: Re: Perhaps a side effect regarding NMI returns

On Tue, 2011-11-29 at 12:44 -0800, Linus Torvalds wrote:
> On Tue, Nov 29, 2011 at 12:35 PM, Steven Rostedt <rostedt@...dmis.org> wrote:

> So I really think this might be a real issue. And the simplest
> approach seems to be to just remove the code. Something like the
> attached (TOTALLY UNTESTED!) patch.
> 

Linus,

I've tested this patch quite a bit with 'perf top -C 1000' and it holds
up well. Could you give me your Signed-off-by so I can include it into
my patch queue?

Thanks,

-- Steve

 arch/x86/kernel/entry_64.S |   32 --------------------------------
 1 files changed, 0 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index faf8d5e74b0b..3819ea907339 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1489,46 +1489,14 @@ ENTRY(nmi)
 	movq %rsp,%rdi
 	movq $-1,%rsi
 	call do_nmi
-#ifdef CONFIG_TRACE_IRQFLAGS
-	/* paranoidexit; without TRACE_IRQS_OFF */
-	/* ebx:	no swapgs flag */
-	DISABLE_INTERRUPTS(CLBR_NONE)
 	testl %ebx,%ebx				/* swapgs needed? */
 	jnz nmi_restore
-	testl $3,CS(%rsp)
-	jnz nmi_userspace
 nmi_swapgs:
 	SWAPGS_UNSAFE_STACK
 nmi_restore:
 	RESTORE_ALL 8
 	jmp irq_return
-nmi_userspace:
-	GET_THREAD_INFO(%rcx)
-	movl TI_flags(%rcx),%ebx
-	andl $_TIF_WORK_MASK,%ebx
-	jz nmi_swapgs
-	movq %rsp,%rdi			/* &pt_regs */
-	call sync_regs
-	movq %rax,%rsp			/* switch stack for scheduling */
-	testl $_TIF_NEED_RESCHED,%ebx
-	jnz nmi_schedule
-	movl %ebx,%edx			/* arg3: thread flags */
-	ENABLE_INTERRUPTS(CLBR_NONE)
-	xorl %esi,%esi 			/* arg2: oldset */
-	movq %rsp,%rdi 			/* arg1: &pt_regs */
-	call do_notify_resume
-	DISABLE_INTERRUPTS(CLBR_NONE)
-	jmp nmi_userspace
-nmi_schedule:
-	ENABLE_INTERRUPTS(CLBR_ANY)
-	call schedule
-	DISABLE_INTERRUPTS(CLBR_ANY)
-	jmp nmi_userspace
 	CFI_ENDPROC
-#else
-	jmp paranoid_exit
-	CFI_ENDPROC
-#endif
 END(nmi)
 
 ENTRY(ignore_sysret)




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