From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by ozlabs.org (Postfix) with ESMTP id 4C23A2C00BA for ; Thu, 3 Oct 2013 00:38:11 +1000 (EST) Message-ID: <524C2FDB.4080203@redhat.com> Date: Wed, 02 Oct 2013 16:38:19 +0200 From: Paolo Bonzini MIME-Version: 1.0 To: Alexander Graf Subject: Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on some powernv systems References: <5243F933.7000907@redhat.com> <20131001083426.GB27484@concordia> <20131001083908.GA17294@redhat.com> <1380620338.645.22.camel@pasglop> <524AAFAA.3010801@redhat.com> <20131002050940.GA25363@drongo> <524BDD73.3020106@redhat.com> <1380704789.645.57.camel@pasglop> <668E4650-BC22-4CBF-A282-E7875DF29DB6@suse.de> <3CBF5732-E7EE-4C96-8132-6D7B77270DAF@suse.de> <20131002100224.GF17294@redhat.com> <1380722275.12149.28.camel@concordia> <029A8D6C-C23C-42B2-8C26-D76B59E2C9DD@suse.de> <524C2EAE.7090209@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Cc: tytso@mit.edu, kvm@vger.kernel.org, Gleb Natapov , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, herbert@gondor.hengli.com.au, Paul Mackerras , mpm@selenic.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Il 02/10/2013 16:36, Alexander Graf ha scritto: >> > >> > With Michael's earlier patch in this series, the hwrng is accessible by >> > host userspace via /dev/hwrng, no? > Yes, but there's not token from user space that gets passed into the > kernel to check whether access is ok or not. So while QEMU may not have > permission to open /dev/hwrng it could spawn a guest that opens it, > drains all entropy out of it and thus stall other processes which try to > fetch entropy, no? > > Maybe I haven't fully grasped the interface yet though :). Yes, that's right. I don't think it's a huge problem, but it's another point in favor of just doing the hypercall in userspace. Paolo