From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/4] Export offsets of VMCS fields as note information for kdump Date: Wed, 18 Apr 2012 17:06:07 +0300 Message-ID: <4F8ECA4F.7070305@redhat.com> References: <4F84E0DF.8040206@cn.fujitsu.com> <4F8D1F46.3090901@redhat.com> <4F8D9F20.9050507@codemonkey.ws> <4F8EAFF7.2040505@redhat.com> <20120418134743.GA25786@fermat.math.technion.ac.il> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Anthony Liguori , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Nadav Har'El" Return-path: In-Reply-To: <20120418134743.GA25786-QeE623+hzFJ/hwrKWqB9+zWi1Rwp9Q0N+oGz7xIJsNs@public.gmane.org> 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 On 04/18/2012 04:47 PM, Nadav Har'El wrote: > On Wed, Apr 18, 2012, Avi Kivity wrote about "Re: [PATCH 0/4] Export offsets of VMCS fields as note information for kdump": > > Right; they're also not required to be in memory at all - the processor > > can cache them, even for VMCSs that are not active at this time. > > Running VMXOFF at panic time can fix that, but you have to broadcast it > > to all processors, probably using NMI... > > I believe that a VMCLEAR ensures that the VMCS is written back to > memory. KVM uses this fact when migrating a VMCS between two separate > physical CPUs - it runs VMCLEAR on the old CPU, to write the VMCS to > memory, and then VMPTRLD on the new CPU. > > So you don't need to VMXOFF, but do need to VMCLEAR. But there's still > the complication that you mention - you need to do the VMCLEAR on the right > processor... VMCLEAR only clears one VMCS; several may be cached by a processor at one time. Presumably VMXOFF flushes everything. -- error compiling committee.c: too many arguments to function