From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4AB09C04A6B for ; Fri, 10 May 2019 15:59:32 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2175520881 for ; Fri, 10 May 2019 15:59:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2175520881 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:45612 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hP7vn-0001hE-FI for qemu-devel@archiver.kernel.org; Fri, 10 May 2019 11:59:31 -0400 Received: from eggs.gnu.org ([209.51.188.92]:36177) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hP7t2-0007N7-H0 for qemu-devel@nongnu.org; Fri, 10 May 2019 11:56:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hP7t1-0005WN-Kn for qemu-devel@nongnu.org; Fri, 10 May 2019 11:56:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54298) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hP7t1-0005VF-EG for qemu-devel@nongnu.org; Fri, 10 May 2019 11:56:39 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B47977E9C4; Fri, 10 May 2019 15:56:38 +0000 (UTC) Received: from [10.40.205.9] (unknown [10.40.205.9]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1335D66D22; Fri, 10 May 2019 15:56:30 +0000 (UTC) To: =?UTF-8?Q?Daniel_P._Berrang=c3=a9?= References: <20190510102637.10209-1-lvivier@redhat.com> <87zhnuqyu0.fsf@dusky.pond.sub.org> <87991c2b-da9d-0e7f-bc09-9fbadbda4ef8@redhat.com> <20190510153227.GO7671@redhat.com> From: Laurent Vivier Message-ID: Date: Fri, 10 May 2019 17:56:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20190510153227.GO7671@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Fri, 10 May 2019 15:56:38 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2] rng-builtin: add an RNG backend that uses qemu_guest_getrandom() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kashyap Chamarthy , Markus Armbruster , Amit Shah , Richard Henderson , qemu-devel@nongnu.org, "Richard W . M . Jones" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/05/2019 17:32, Daniel P. Berrang=C3=A9 wrote: > On Fri, May 10, 2019 at 02:37:41PM +0200, Laurent Vivier wrote: >> On 10/05/2019 14:27, Markus Armbruster wrote: >>> Laurent Vivier writes: >>> The new rng-builtin is considerably simpler than both rng-random and >>> rng-egd. Moreover, it just works, whereas rng-random is limited to >>> CONFIG_POSIX, and rng-egd needs egd running (which I suspect basicall= y >>> nobody does). Have we considered deprecating these two backends in >>> favor of rng-builtin? >> >> I have several bugzilla involving these backends: as there are blockin= g, the >> virtio-rng device in the guest can hang, or crash during hot-unplug. F= rom my >> point of view, life would be easier without them... >=20 > Are you sure about that ? >=20 > The EGD impl looks like it is requesting entropy in an async manner. The virtio-rng driver waits until it receives enough entropy from the=20 RNG backend while a mutex is taken. If the EGD daemon doesn't provide enough data to the RNG backend,=20 virtio-rng driver can hang. It's easy to have if we start EGD backend with a socket in server,nowait=20 mode and no EGD daemon connects to the port. Thanks, Laurent