From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support
 infrastructure
Date: Tue, 30 Jan 2018 20:46:23 +0000
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Cc: David Woodhouse <dwmw2@infradead.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Eduardo Habkost <ehabkost@redhat.com>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Lau
To: Linus Torvalds <torvalds@linux-foundation.org>
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> If you are ever going to migrate to Skylake, I think you should just
> always tell the guests that you're running on Skylake. That way the
> guests will always assume the worst case situation wrt Specte.

Unfortunately if you do that then guest may also decide to use other
Skylake hardware features and pop its clogs when it finds out its actually
running on Westmere or SandyBridge.

So you need to be able to both lie to the OS and user space via cpuid and
also have a second 'but do skylake protections' that only mitigation
aware software knows about.

Alan