linux-kernel - Re: [RFC PATCH v2 3/6] x86/pti: add a per-cpu variable pti

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Message-ID: <20180110080102.7ggggtruidb53yfu@gmail.com>
Date:   Wed, 10 Jan 2018 09:01:02 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Willy Tarreau <w@....eu>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH v2 3/6] x86/pti: add a per-cpu variable pti_disable


* Willy Tarreau <w@....eu> wrote:

> [...] If we had "pit_enabled", something like this could be confusing because 
> it's not obvious whether this pti_enabled *enforces* PTI or if its absence 
> disables it :
> 
> 	cmpb $0, PER_CPU_VAR(pti_enabled)
> 	jz .Lend\@

The natural sequence would be:

	cmpb $1, PER_CPU_VAR(pti_enabled)
	jne .Lend\@

which is not confusing to me at all.

Thanks,

	Ingo