From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x224sj4gAxAgxYDjhZlstsNWvdQZ7AhQP9MxKtftLRW7wyvVNMtdsEVgv3qSfoJPyepNhvBX6 ARC-Seal: i=1; a=rsa-sha256; t=1517313378; cv=none; d=google.com; s=arc-20160816; b=yIp1GATFFfq76+a/fkL2g9VNDAt3cAdhBNoD00HoyTHg3chLqYSCT9C5qUAv6fRzqC DmZSQPWfN9woRXzFADnG86zgV6tPNw3fIxnPYb2r15/4WHt5nt+nODds+h4vLMptC5e6 awl8p48g+v5GFMHz3EQwlUW0OjDRnyW6IvDAQNLJUOuXgIIj85KuN2CHGzSgJ8gYqhSQ B1CR+q/nzfEXldZJNMpacaFKQbdJ06vu8D+kqYLWS/E1vDdm9Xjb8Lt8vmawztflCvGi NqIYvyRFcDOyb/RXl5iS1oKAwFMhmt8fHdJlZzAgCuwlQBDuuxbwuA5uiBaIBAtTbro9 hBUg== 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=n9nWzTQyS20f03G8wIxZKXB0B1cn4X4ifkKVviUa/sE=; b=nLKsgNrzUnhIU9u+aPhGw4R8TQhat8Zk+hmHTTi2qYR1znkWUHFZVpLrFZriO84o1g +6M5W2nA0hm6mZm2CEjbfTxJ4M6V423rWM0/6sOrB57QXwtcKKfQHKPIn+iEGFYXqmuZ rwmAALqWwySIfp5MNPy5Of8qkAsJ21In9YmP6hurXEpSDBuIUWdn2EPk4xZqCqQP6+YA urMEQjnpNKz7PV+YSZo0DuTqMTyH8G6LZSg1ROv+K0Ql9HXPqsWA8GxCwZh2OX6CGKf2 prFFH3DKgSluhJsLvE5i7mAzbuAQLGIYh5F12qnojNKyaSwDlcldcTdkTPigZAUpvQDE V95w== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of dgilbert@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=dgilbert@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 dgilbert@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=dgilbert@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Date: Tue, 30 Jan 2018 11:56:09 +0000 From: "Dr. David Alan Gilbert" To: Linus Torvalds Cc: David Woodhouse , Arjan van de Ven , Eduardo Habkost , KarimAllah Ahmed , Linux Kernel Mailing List , 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 , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Gleixner , Tim Chen , Tom Lendacky , KVM list , the arch/x86 maintainers Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support infrastructure Message-ID: <20180130115608.GA2537@work-vm> 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: 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?1591018393273842951?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: * Linus Torvalds (torvalds@linux-foundation.org) wrote: > Why do you even _care_ about the guest, and how it acts wrt Skylake? > What you should care about is not so much the guests (which do their > own thing) but protect guests from each other, no? > > So I'm a bit mystified by some of this discussion within the context > of virtual machines. I think that is separate from any measures that > the guest machine may then decide to partake in. Because you'd never want to be the cause of the guest making the wrong decision and thus being less secure than it was on real hardware. > 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. Say you've got a pile of Ivybridge, all running lots of VMs, the guests see that they're running on Ivybridge. Now you need some more hosts, so you buy the latest Skylake boxes, and add them into your cluster. Previously it was fine to live migrate a VM to the Skylake box and the VM still sees it's running Ivybridge; and you can migrate that VM back and forward. The rule was that as long as the CPU type you told the guest was old enough then it could migrate to any newer box. You can't tell the VMs running on Ivybridge they're running on Skylake otherwise they'll start trying to use Skylake features (OK, they should be checking flags, but that's a separate story). Dave > Maybe that mystification comes from me missing something. > > Linus -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK