From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/2] KVM: Protect race-condition between VMCS and current_vmcs on VMX hardware Date: Thu, 26 Jul 2007 19:31:52 +0300 Message-ID: <46A8CC78.8060509@qumranet.com> References: <46A882480200005A00028358@mcclure.wal.novell.com> <46A8BF26.5030802@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Gregory Haskins Return-path: In-Reply-To: <46A8BF26.5030802-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Avi Kivity wrote: >> >> Sure. It can happen with two VMs are running simultaneously. Lets call >> them VM-a and VM-b. Assume the scenario: VM-a is on CPU-x, gets >> migrated to CPU-y, and VM-b gets scheduled in on CPU-x. There is a race >> on CPU-x with the VMCS handling logic between the VM-b process context, >> and the IPI to execute the __vcpu_clear for VM-a. >> > > A race indeed, good catch. > > I think the race is only on the per_cpu(current_vmcs) variable, no? > The actual vmcs ptr (as loaded by vmptrld) is handled by the processor. btw, I think the race is benign. if __vcpu_clear() wins, vcpu_load() gets to set current_vmcs and all is well. If vcpu_load() wins, __vcpu_clear() stomps on current_vmcs, but the only effect of that the next time vcpu_load() is called, it issues an unnecessary vmptrld. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/