From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751942AbaEATqV (ORCPT ); Thu, 1 May 2014 15:46:21 -0400 Received: from terminus.zytor.com ([198.137.202.10]:39951 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751867AbaEATqT (ORCPT ); Thu, 1 May 2014 15:46:19 -0400 User-Agent: K-9 Mail for Android In-Reply-To: <20140501192618.GA25829@thunk.org> References: <20140501192618.GA25829@thunk.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Subject: Re: random: Providing a seed value to VM guests From: "H. Peter Anvin" Date: Thu, 01 May 2014 12:40:35 -0700 To: tytso@mit.edu, Andy Lutomirski CC: Florian Weimer , "linux-kernel@vger.kernel.org" , Kees Cook , kvm list Message-ID: <068139e3-50f8-4d44-972a-0296b6bc36f7@email.android.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As I said... I think KVM has already added an emulated instructions enumeration API. On May 1, 2014 12:26:18 PM PDT, tytso@mit.edu wrote: >On Thu, May 01, 2014 at 12:02:49PM -0700, Andy Lutomirski wrote: >> >> Is RDSEED really reasonable here? Won't it slow down by several >> orders of magnitude? > >That is I think the biggest problem; RDRAND and RDSEED are fast if >they are native, but they will involve a VM exit if they need to be >emulated. So when an OS might want to use RDRAND and RDSEED might be >quite different if we know they are being emulated. > >Using the RDRAND and RDSEED "api" certainly makes sense, at least for >x86, but I suspect we might want to use a different way of signalling >that a VM guest can use RDRAND and RDSEED if they are running on a CPU >which doesn't provide that kind of access. Maybe a CPUID extended >function parameter, if one could be allocated for use by a Linux >hypervisor? > > - Ted -- Sent from my mobile phone. Please pardon brevity and lack of formatting.