Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753492Ab3JAJ72 (ORCPT ); Tue, 1 Oct 2013 05:59:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:29619 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752799Ab3JAJ7Z (ORCPT ); Tue, 1 Oct 2013 05:59:25 -0400 Date: Tue, 1 Oct 2013 12:57:59 +0300 From: Gleb Natapov To: Paul Mackerras Cc: Michael Ellerman , Paolo Bonzini , linux-kernel@vger.kernel.org, Benjamin Herrenschmidt , agraf@suse.de, mpm@selenic.com, herbert@gondor.hengli.com.au, linuxppc-dev@ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, tytso@mit.edu Subject: Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on some powernv systems Message-ID: <20131001095759.GA1308@redhat.com> References: <1380177066-3835-1-git-send-email-michael@ellerman.id.au> <1380177066-3835-3-git-send-email-michael@ellerman.id.au> <5243F933.7000907@redhat.com> <20131001083426.GB27484@concordia> <20131001083908.GA17294@redhat.com> <20131001092320.GA2000@iris.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131001092320.GA2000@iris.ozlabs.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1405 Lines: 33 On Tue, Oct 01, 2013 at 07:23:20PM +1000, Paul Mackerras wrote: > On Tue, Oct 01, 2013 at 11:39:08AM +0300, Gleb Natapov wrote: > > On Tue, Oct 01, 2013 at 06:34:26PM +1000, Michael Ellerman wrote: > > > On Thu, Sep 26, 2013 at 11:06:59AM +0200, Paolo Bonzini wrote: > > > > Il 26/09/2013 08:31, Michael Ellerman ha scritto: > > > > > Some powernv systems include a hwrng. Guests can access it via the > > > > > H_RANDOM hcall. > > > > > > > > Is there any reason to do this in the kernel? > > > > > > It's less code, and it's faster :) > > > > > > > It does not have to be a particularly fast path; > > > > > > Sure, but do we have to make it slow on purpose? > > > > > We do not put non performance critical devices into the kernel. > > It's not a device, it's a single hypercall, specified by PAPR, which > is the moral equivalent of x86's RDRAND. > OK. A couple of general questions. How guest knows when this hypercall is available? Is QEMU enable it when KVM_CAP_PPC_HWRNG is available (I haven't seen userspace patch that uses KVM_CAP_PPC_HWRNG)? What about QEMU TCG does it implement this hypercall or it emulates hwrng directly? -- Gleb. -- 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/