From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 08/16] x86: Emergency virtualization disable function Date: Sun, 09 Nov 2008 13:23:14 +0200 Message-ID: <4916C822.4080609@redhat.com> References: <1225810364-8990-1-git-send-email-ehabkost@redhat.com> <1225810364-8990-9-git-send-email-ehabkost@redhat.com> <20081105175235.GJ5247@blackpad> <4912BD67.8000704@redhat.com> <4912C75B.8050508@redhat.com> <20081106174538.GU5247@blackpad> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Andrew Morton , kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "Rafael J. Wysocki" , Haren Myneni , Simon Horman , "Eric W. Biederman" , Ingo Molnar , Andrey Borzenkov , mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Vivek Goyal To: Eduardo Habkost Return-path: In-Reply-To: <20081106174538.GU5247@blackpad> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kexec-bounces-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Errors-To: kexec-bounces+glkk-kexec=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: kvm.vger.kernel.org Eduardo Habkost wrote: > On Thu, Nov 06, 2008 at 12:30:51PM +0200, Avi Kivity wrote: > >> Eric W. Biederman wrote: >> >>>> If you want to be extra simple and safe, remove kvm from the equation. Make the >>>> disabling code part of kdump/emergency_restart and only rely on the convention >>>> that cr3.vmxe == vmxon. >>>> >>>> >>> Convention? >>> >>> >> There is a de-facto convention supported by at least vmware and kvm. If >> cr4.vmxe is 1, then we are in vmx operation. If cr4.vmxe is 0, then we >> are not in vmx operation. This allows us to determine whether we need >> to execute vmxoff without any APIs. >> > > I am just worried about the probing needed to make sure CR4 is available > (and that the CR4.VMXE bit means what we expect it to mean), That's cpu_has_kvm_support() in vmx.c. Should compile to three instructions. > before we > try to read it and check VMXE. The same for SVM and the MSRs we need to > touch to disable SVM. > That's has_svm() in svm.c; slightly longer but not any more dangerous. > I prefer to reuse code that already exists on KVM and is working than > adding new probing code that I won't be able to test on all hardware > configurations. > We could move the code to a header file, and so compile it both for kvm and for emergency_restart/kdump. -- error compiling committee.c: too many arguments to function