linux-kernel - Re: [RFC][PATCH] x86: proposed new ARCH_CAPABILITIES MSR bit for RSB-underflow

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Date:   Fri, 16 Feb 2018 11:47:27 -0800
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Rik van Riel <riel@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jikos@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Kees Cook <keescook@...gle.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Paul Turner <pjt@...gle.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Mallick, Asit K" <asit.k.mallick@...el.com>
Subject: Re: [RFC][PATCH] x86: proposed new ARCH_CAPABILITIES MSR bit for
 RSB-underflow

On 2/16/2018 11:43 AM, Linus Torvalds wrote:
> On Fri, Feb 16, 2018 at 11:38 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> Of course, your patch still doesn't allow for "we claim to be skylake
>> for various other independent reasons, but the RSB issue is fixed".
> 
> .. maybe nobody ever has a reason to do that, though?

yeah I would be extremely surprised
> 
> Who knows, virtualization people may simply want the user to specify
> the model, but then make the Spectre decisions be based on actual
> hardware capabilities (whether those are "current" or "some minimum
> base").

once you fake to be skylake when you're not, you do that for a reason; normallyt
that reason is that you COULD migrate to a skylake.
(and migration is not supposed to be visble to the guest OS)

and at that point you are a skylake for all intents and purposes.

(and the virtualization people also really hate it when the hardware
burst the bubble of this fakeing hardware to be not what it is)