From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:53736) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TTZ56-0000uj-08 for qemu-devel@nongnu.org; Wed, 31 Oct 2012 10:15:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TTZ4r-0003EM-Uq for qemu-devel@nongnu.org; Wed, 31 Oct 2012 10:15:43 -0400 Received: from terminus.zytor.com ([198.137.202.10]:47867 helo=mail.zytor.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TTZ4r-0003D7-MB for qemu-devel@nongnu.org; Wed, 31 Oct 2012 10:15:29 -0400 Message-ID: <50913273.5010502@zytor.com> Date: Wed, 31 Oct 2012 07:15:15 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 References: <604401631.2277495.1351264128301.JavaMail.root@redhat.com> <871ugl44v5.fsf@codemonkey.ws> <508AB5C0.2000304@zytor.com> <508ADD66.5040909@redhat.com> <5ea4bbfb-b761-42ef-93f8-7c91fee0bb30@email.android.com> <508AE9A6.4060304@redhat.com> <508AF2C0.30404@zytor.com> <508E4215.6050803@redhat.com> <508F5B07.8070008@zytor.com> <508F9847.6030702@redhat.com> <50904273.5040401@zytor.com> <5090D36C.9080807@redhat.com> In-Reply-To: <5090D36C.9080807@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 0/6] add paravirtualization hwrng support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Amit Shah , Anthony Liguori , Andreas Faerber , qemu-devel@nongnu.org On 10/31/2012 12:29 AM, Paolo Bonzini wrote: > > Related to this, rdrand's "entropy content" in the worst case will be > only 1/255th of the data it produces: Intel documents that one 256-bit > seed will result in up to 1022 64-bit random numbers. Yet, it is good > enough to drive rngd. Would it make sense for QEMU to implement the > same kind of stretching of /dev/random data, to avoid depleting the > host's entropy pool too fast? > Absolutely not; in fact, we have to do data reduction in rngd for exactly this reason (and a Qemu backend would have to do the same). There is a new RDSEED instruction in newer CPUs to correct this. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.