From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: drop -enable-nesting Date: Mon, 30 May 2011 17:27:33 +0200 Message-ID: <4DE3B765.8000806@siemens.com> References: <4DDAD5CF.5050805@redhat.com> <4DE0B4B1.1000407@web.de> <20110530081847.GC27062@amd.com> <4DE3A3EC.80201@siemens.com> <20110530143846.GA2957@fermat.math.technion.ac.il> <4DE3B1E2.7020006@siemens.com> <20110530151020.GB7855@amd.com> <4DE3B4A5.6050509@siemens.com> <4DE3B572.6030105@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: Anthony Liguori , Nadav Har'El , kvm , john cooper , "Roedel, Joerg" , "qemu-devel@nongnu.org" To: Avi Kivity Return-path: In-Reply-To: <4DE3B572.6030105@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org On 2011-05-30 17:19, Avi Kivity wrote: > On 05/30/2011 06:15 PM, Jan Kiszka wrote: >> On 2011-05-30 17:10, Roedel, Joerg wrote: >>> On Mon, May 30, 2011 at 11:04:02AM -0400, Jan Kiszka wrote: >>>> On 2011-05-30 16:38, Nadav Har'El wrote: >>>>> On Mon, May 30, 2011, Jan Kiszka wrote about "drop -enable-nesting= (was: [PATCH 3/7] cpu model bug fixes and definition corrections...)": >>>>>> On 2011-05-30 10:18, Roedel, Joerg wrote: >>>>>>> On Sat, May 28, 2011 at 04:39:13AM -0400, Jan Kiszka wrote: >>>>>>> >>>>>>>> J=EF=BF=BDrg, how to deal with -enable-nesting in qemu-kvm to a= lign behavior >>>>>>>> with upstream? >>>>>>> >>>>>>> My personal preference is to just remove it. In upstream-qemu it= is >>>>>>> enabled/disabled by +/-svm. -enable-nesting is just a historic t= hing >>>>>>> which can be wiped out. >>>>> >>>>> "-enable-nesting" could remain as a synonym for enabling either VM= X or SVM >>>>> in the guest, depending on what was available in the host (because= KVM now >>>>> supports both nested SVM and nested VMX, but not SVM-on-VMX or vic= e versa). >>>> >>>> Why? Once nesting is stable (I think SVM already is), there is no r= eason >>>> for an explicit enable. And you can always mask it out via -cpu. >>>> >>>> BTW, what are the defaults for SVM right now in qemu-kvm and upstre= am? >>>> Enable if the modeled CPU supports it? >>> >>> qemu-kvm still needs -enable-nesting, otherwise it is disabled. Upst= ream >>> qemu should enable it unconditionally (can be disabled with -cpu ,-s= vm). >> >> Then let's start with aligning qemu-kvm defaults to upstream? I guess >> that's what the diff I was citing yesterday is responsible for. >> >> In the same run, -enable-nesting could dump a warning on the console >> that this switch is obsolete and will be removed from future versions. >=20 > I think it's safe to drop -enable-nesting immediately. Dan, does=20 > libvirt make use of it? I'm currently checking with some customer who played with Proxmox and nesting if that stack was aware of the switch or accepted it only via a side channel. >=20 >> For VMX, I would suggest to keep it off by default until it matured, >> asking the user to issue -cpu ...,+vmx. >=20 > We should do that for svm as well (except for -cpu host or -cpu=20 > something-with-svm). I assume that's what upstream is doing. Maybe it has it was part of the artificial default qemu64 model which is AMD based. > vmx will be kept disabled by the module option,=20 > until it is deemed fit for general consumption. >=20 Yes, even better - no need for duplicate controls. Jan --=20 Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux