linux-kernel - Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec

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Message-ID: <CA+55aFzSYExr33w849=3o+2XGr9pUKpFucc5p-kKbEy20VVLPA@mail.gmail.com>
Date:   Wed, 3 Jan 2018 16:39:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arch@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Alan Cox <alan@...ux.intel.com>
Subject: Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier

On Wed, Jan 3, 2018 at 4:15 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> The 'if_nospec' primitive marks locations where the kernel is disabling
> speculative execution that could potentially access privileged data. It
> is expected to be paired with a 'nospec_{ptr,load}' where the user
> controlled value is actually consumed.

I'm much less worried about these "nospec_load/if" macros, than I am
about having a sane way to determine when they should be needed.

Is there such a sane model right now, or are we talking "people will
randomly add these based on strong feelings"?

                    Linus