Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752217AbaGPUVS (ORCPT ); Wed, 16 Jul 2014 16:21:18 -0400 Received: from terminus.zytor.com ([198.137.202.10]:45197 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171AbaGPUVP (ORCPT ); Wed, 16 Jul 2014 16:21:15 -0400 Message-ID: <53C6DEA5.7010203@zytor.com> Date: Wed, 16 Jul 2014 13:20:53 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Gleb Natapov CC: Paolo Bonzini , Andy Lutomirski , Daniel Borkmann , kvm list , "Theodore Ts'o" , "linux-kernel@vger.kernel.org" , Kees Cook , X86 ML , Srivatsa Vaddagiri , Raghavendra K T Subject: Re: [PATCH 0/4] random,x86,kvm: Add and use MSR_KVM_GET_RNG_SEED References: <20140716064110.GV18167@minantech.com> <53C62563.6050106@redhat.com> <53C62B68.50702@redhat.com> <53C6A236.7040904@zytor.com> <53C6A362.7090709@redhat.com> <53C6A4A3.1040702@zytor.com> <20140716162133.GO4399@minantech.com> In-Reply-To: <20140716162133.GO4399@minantech.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/16/2014 09:21 AM, Gleb Natapov wrote: > On Wed, Jul 16, 2014 at 09:13:23AM -0700, H. Peter Anvin wrote: >> On 07/16/2014 09:08 AM, Paolo Bonzini wrote: >>> Il 16/07/2014 18:03, H. Peter Anvin ha scritto: >>>> I suggested emulating RDRAND *but not set the CPUID bit*. We already >>>> developed a protocol in KVM/Qemu to enumerate emulated features (created >>>> for MOVBE as I recall), specifically to service the semantic "feature X >>>> will work but will be substantially slower than normal." >>> >>> But those will set the CPUID bit. There is currently no way for KVM >>> guests to know if a CPUID bit is real or emulated. >>> >> >> OK, so there wasn't any protocol implemented in the end. I sit corrected. >> > That protocol that was implemented is between qemu and kvm, not kvm and a guest. > Either which way, the notion was to have a PV CPUID bit like the proposed kvm_get_rng_seed bit, but to have it exercised by executing RDRAND. The biggest reason to *not* do this would be that with an MSR it is not available to guest user space, which may be better under the circumstances. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/