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Subject: Re: [RFC][PATCH] x86: proposed new ARCH_CAPABILITIES MSR bit for
 RSB-underflow
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Rik van Riel <riel@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jiri Kosina <jikos@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Kees Cook <keescook@google.com>,
        Greg Kroah-Hartman <gregkh@linux-foundation.org>,
        Paul Turner <pjt@google.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        the arch/x86 maintainers <x86@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        "Mallick, Asit K" <asit.k.mallick@intel.com>
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From:   Arjan van de Ven <arjan@linux.intel.com>
Message-ID: <768f3a56-28b0-91a1-f555-94e64a146abc@linux.intel.com>
Date:   Fri, 16 Feb 2018 11:47:27 -0800
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On 2/16/2018 11:43 AM, Linus Torvalds wrote:
> On Fri, Feb 16, 2018 at 11:38 AM, Linus Torvalds
> <torvalds@linux-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)