linux-kernel - Re: [PATCH RFC 2/4] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET

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Message-ID: <20180108171943.GC6176@hirez.programming.kicks-ass.net>
Date:   Mon, 8 Jan 2018 18:19:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Willy Tarreau <w@....eu>, linux-kernel@...r.kernel.org,
        x86@...nel.org, tglx@...utronix.de, gnomes@...rguk.ukuu.org.uk,
        torvalds@...ux-foundation.org, Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH RFC 2/4] x86/arch_prctl: add ARCH_GET_NOPTI and
 ARCH_SET_NOPTI to enable/disable PTI

On Mon, Jan 08, 2018 at 06:05:31PM +0100, Ingo Molnar wrote:
> Note that there is somewhat of a fuzzy detail regarding AMD CPUs which are marked 
> as 'Meltdown safe': should an explicit request to turn on PTI be honored by the 
> kernel? Should that be some sort of separate 'force PTI on' attribute?

AMD should not have FEATURE_PTI enabled, and thus not end up in any code
that cares about TIF_NOPTI.