From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gnomes@lxorguk.ukuu.org.uk>
X-Google-Smtp-Source: AH8x226ZgTU5obXXKN2aRYtdYWlk1DBhGJ/N5hH4LpjiBQU+lq3893/q+FkvdlI5aNC5dP7dUqE2
ARC-Seal: i=1; a=rsa-sha256; t=1517345218; cv=none;
        d=google.com; s=arc-20160816;
        b=fhyWusSUTu6aZgCCCBt+HfMXQZ35xIXNTIZvbKgsRnLBaUtbKnDr1CDvAAaRsjN95v
         bOmQqx8PTG+bo8qyoW4zoZh9xUqmdx0XEiXVSxUJcd09TRJlF4ysVJmUwUHdmZJzjEys
         eGbHefJA4aBazXLelPLvynbPQqUB8tAFRpt+azw30Q3xIAdGY3x1osyxZ6M8l8t+zJT9
         5GfgxWl5OYDiDN0II8IfJ9IVjorF4GS1vUOI7cKBbC2G17kAV63O2rXBm6DiNDVPHc4z
         a58SycsyhZlL8dhOUXXDisFwhJuyQ4VGPznW13sL5vMiVeSqeHDN18SigHQdltzcqkvF
         /BRA==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
        h=content-transfer-encoding:mime-version:organization:references
         :in-reply-to:message-id:subject:cc:to:from:date
         :arc-authentication-results;
        bh=BVNbPQ0qtdP+6+y1GYRythYqI6fZXNfHLxNcid/j2+c=;
        b=BiHIE61JlFB7ktcR2FRGtbMUkks7hlZhGkIzg5w2ih0u+kh0kf4bQ7dBg0wnzbI97y
         /PnzKVvPpCL7goTwl1rzx8K7ReTfUagrUZfgQDT9RlUUKFvHrBjgFrc2RPJ+4hv+aR7V
         yvXT/AKu3BrxWwdOJJ2g7SR/TwRxQBOkGAAgs1MMVDLUCiV+o6+tui7Md520FgyGI5Uf
         jbvCw0sdF32FsiFu+9PRB95AlpxX6OOjnA3oRy7Op5lBqMZLHmoGO4NQGGHEgoI1CmRE
         dAoOSC6wzEHUjzdoOeHLc3iA4RhVD+sr2Rl4kj5F53ffvT4I/oto+v+EtC9oSd3jIrSb
         o1hQ==
ARC-Authentication-Results: i=1; mx.google.com;
       spf=pass (google.com: domain of gnomes@lxorguk.ukuu.org.uk designates 82.70.14.225 as permitted sender) smtp.mailfrom=gnomes@lxorguk.ukuu.org.uk
Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of gnomes@lxorguk.ukuu.org.uk designates 82.70.14.225 as permitted sender) smtp.mailfrom=gnomes@lxorguk.ukuu.org.uk
Date: Tue, 30 Jan 2018 20:46:23 +0000
From: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
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>,
        Laura Abbott <labbott@redhat.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Paolo Bonzini
 <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Radim
 =?UTF-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Thomas Gleixner
 <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky
 <thomas.lendacky@amd.com>,
        KVM list <kvm@vger.kernel.org>,
        "the arch/x86
 maintainers" <x86@kernel.org>,
        "Dr. David Alan Gilbert"
 <dgilbert@redhat.com>
Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support
 infrastructure
Message-ID: <20180130204623.583b1a7a@alans-desktop>
In-Reply-To: <CA+55aFxBh3LvsQq9wy313NQCn3iu+yuAmsi0zNVxWmGDUUds-A@mail.gmail.com>
References: <1516476182-5153-6-git-send-email-karahmed@amazon.de>
	<20180129201404.GA1588@localhost.localdomain>
	<1517257022.18619.30.camel@infradead.org>
	<20180129204256.GV25150@localhost.localdomain>
	<31415b7f-9c76-c102-86cd-6bf4e23e3aee@linux.intel.com>
	<1517259759.18619.38.camel@infradead.org>
	<CA+55aFxBh3LvsQq9wy313NQCn3iu+yuAmsi0zNVxWmGDUUds-A@mail.gmail.com>
Organization: Intel Corporation
X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-getmail-retrieved-from-mailbox: INBOX
X-GMAIL-THRID: =?utf-8?q?1590140581449802182?=
X-GMAIL-MSGID: =?utf-8?q?1591051779456192878?=
X-Mailing-List: linux-kernel@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>

> 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