From mboxrd@z Thu Jan 1 00:00:00 1970 From: poma Subject: Re: KVM SVM(AMD) nested - disabled by default? Date: Mon, 25 Jan 2016 19:31:14 +0100 Message-ID: <56A669F2.1050905@gmail.com> References: <56A39729.8020106@gmail.com> <56A3EB1C.5020605@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: kvm-devel , Joerg Roedel , Avi Kivity , Cole Robinson , "Richard W.M. Jones" To: Paolo Bonzini Return-path: Received: from mail-wm0-f49.google.com ([74.125.82.49]:34864 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932779AbcAYSbS (ORCPT ); Mon, 25 Jan 2016 13:31:18 -0500 Received: by mail-wm0-f49.google.com with SMTP id r129so75724351wmr.0 for ; Mon, 25 Jan 2016 10:31:17 -0800 (PST) In-Reply-To: <56A3EB1C.5020605@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 23.01.2016 22:05, Paolo Bonzini wrote: > > > On 23/01/2016 16:07, poma wrote: >> "KVM: SVM: enable nested svm by default" >> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/arch/x86/kvm?id=4b6e4dc >> "Nested SVM is (in my experience) stable enough to be enabled by default. So omit the requirement to pass a module parameter." >> >> I tried to get an explanation of the eventual -default- change here: >> https://bugzilla.redhat.com/show_bug.cgi?id=1298244 >> >> but "... I am *thinking* of changing it ..." ain't explanation, man. >> >> I've tested "Nested SVM" myself and it works surprisingly well, >> therefore what is the -actual- reason to switch it off by default? > > Neither nested VMX nor nested SVM have ever been audited for security; > they could have bugs that let a malicious guest escape L0. In fact I > would be surprised if they don't. :( > > Paolo > "In nested virtualization, we have three levels: The host (KVM), which we call L0, the guest hypervisor, which we call L1, and its nested guest, which we call L2." https://www.kernel.org/doc/Documentation/virtual/kvm/nested-vmx.txt So as long as you don't nestle proprietary crap, no problemos. Thanks for the concise explanations, man.