linux-kernel - Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

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Date:   Tue, 5 Feb 2019 18:09:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

On Tue, Feb 05, 2019 at 08:46:23AM -0800, Dave Hansen wrote:
> On 2/4/19 10:18 PM, Borislav Petkov wrote:

> > Well, if it breaks old apps, it probably needs to be opt-in anyway.
> 
> Yes, this was my assumption.

It _should_ not break portable code (because RISC has much stronger #AC
requirements).

That said; I really do think we want it default enabled and allow
individual apps to opt-out with a system-wide override to disable the
opt-out.

The cloud vendors and RT thingies will want to disable the opt-out for
example.