Date: Wed, 1 Apr 2015 11:45:49 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@amacapital.net>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/asm/entry/64: fold test_in_nmi macro into its only
 user
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On Wed,  1 Apr 2015 16:50:57 +0200
Denys Vlasenko <dvlasenk@redhat.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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