linux-kernel - Re: [PATCH] x86/asm/entry/64: fold test_in

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Date:	Wed, 1 Apr 2015 11:45:49 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/asm/entry/64: fold test_in_nmi macro into its only
 user

On Wed,  1 Apr 2015 16:50:57 +0200
Denys Vlasenko <dvlasenk@...hat.com> wrote:

> -	/* runs on exception stack */
> +/* Runs on exception stack */
>  ENTRY(nmi)
>  	INTR_FRAME
>  	PARAVIRT_ADJUST_EXCEPTION_FRAME
> @@ -1428,8 +1416,18 @@ ENTRY(nmi)
>  	 * We check the variable because the first NMI could be in a
>  	 * breakpoint routine using a breakpoint stack.
>  	 */
> -	lea 6*8(%rsp), %rdx
> -	test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
> +	lea	6*8(%rsp), %rdx
> +	/* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */
> +	cmpq	%rdx, 4*8(%rsp)
> +	/* If the stack pointer is above the NMI stack, this is a normal NMI */
> +	ja	first_nmi
> +	subq	$EXCEPTION_STKSZ, %rdx
> +	cmpq	%rdx, 4*8(%rsp)
> +	/* If it is below the NMI stack, it is a normal NMI */
> +	jb	first_nmi
> +	/* Ah, it is within the NMI stack, treat it as nested */
> +	jmp	nested_nmi

I guess we can get rid of the jmp nested_nmi, as it just jumps to the
next instruction. Although, I would keep the comment.

-- Steve

> +
>  	CFI_REMEMBER_STATE
>  
>  nested_nmi:

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