From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x2277W9+pWOTVX4fogmiz5OoU4c+7dEMiylNd/8t60T0S4TsRleVhiqrX7G0pWVQBIbZiK1QG ARC-Seal: i=1; a=rsa-sha256; t=1517262628; cv=none; d=google.com; s=arc-20160816; b=bNAlLLpzngztpgcu8Asd6QFOVXbmpPM03BPtip3hkboOzjxauK9cslqXANTl00s09k DDfoKEvtT0RPZ1hbrJG9CrP8fOgT4KnIGXzvf9AqiGjgieO2QajuS6ijvLk91hd+Dwrg WLcnbi6M/itFNTCL16ZLJLQfUd1QZ8z3FMlUkY6TI6MLr3zEYmy9zz7KUIrVy+kpF0Bi ZInfDhxTn6HihBG+hs8wCOj9QqXrpFbfoM7JhDAOKKgY1mtfVa5/8/9AOY6YJ7++pJy+ zsaWwtF/5qdDXU15SAtLwdD8fSjoXsNpVISKl2W1JoAkEY3P5pKUP1KnfDmJFl68qOP3 9rPw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:arc-authentication-results; bh=kUrlOnwJ2Qyknu7+y0n1Z/BOVXjCLIqaLlCcS6InlZ4=; b=tGxPlVR3Df0kNuyeWtS+7suEET25Ek/3LHGjll6tRE99Lq3+wVEMnSwkdP8/uVdEeM qcYfs12joxOXc04x0EOC4sSSj6QXnLNi8C55vAD2nzPiNztnkeCkvg0mmnkyeXiS6mcZ jMLBw6DfpEp30R1QoXp/+ljLAnCQlJDkp1IFuhV7aYpOAxaZFVGjUaaxRPXZpauyHP0M FxLACL/v4EDDS/cIjUuWTaH4myd0CpO5SK/i7tcxXp8wgR1bxvCA0FnVd+iAZWzEGaIb lGvmf7DmX7J16Rg9bypiDIdBrfGeQF9U2dq69kez3+fcB610iO1ycQ64dbDyFoMPBZgm WPmA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of ehabkost@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=ehabkost@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of ehabkost@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=ehabkost@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Date: Mon, 29 Jan 2018 19:50:25 -0200 From: Eduardo Habkost To: Jim Mattson Cc: David Woodhouse , Arjan van de Ven , KarimAllah Ahmed , LKML , Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Linus Torvalds , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Gleixner , Tim Chen , Tom Lendacky , kvm list , the arch/x86 maintainers , "Dr. David Alan Gilbert" Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support infrastructure Message-ID: <20180129215025.GX25150@localhost.localdomain> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Fnord: you can see the fnord User-Agent: Mutt/1.9.1 (2017-09-22) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140581449802182?= X-GMAIL-MSGID: =?utf-8?q?1590965177979483231?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Mon, Jan 29, 2018 at 01:37:05PM -0800, Jim Mattson wrote: > For GCE, "you might be migrated to Skylake" is pretty much a > certainty. Even if you're in a zone that doesn't currently have > Skylake machines, chances are pretty good that it will have Skylake > machines some day in the not-too-distant future. This kind of scenario is why I suggest a "we promise you're not going to be migrated to Skylake" bit instead a "you may be migrated to Skylake" bit. The hypervisor could prevent migration to Skylake hosts if management software chose to enable this bit, and guests would choose the safest option (i.e. assume the worst) if running on older hypervisors that don't set the bit. > > In general, making these kinds of decisions based on F/M/S is probably > unwise when running in a VM. Certainly. That's why I suggest not trusting f/m/s unless the hypervisor is explicitly saying it's accurate. -- Eduardo