On Wed, Nov 28, 2012 at 08:54:14PM +0800, Xiao Guangrong wrote: > vmcs->cpu indicates whether it exists on the target cpu, -1 means the vmcs > does not exist on any vcpu > > If vcpu load vmcs with vmcs.cpu = -1, it can be directly added to cpu's percpu > list. The list can be corrupted if the cpu prefetch the vmcs's list before > reading vmcs->cpu. Meanwhile, we should remove vmcs from the list before > making vmcs->vcpu == -1 be visible > > Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> > --- > arch/x86/kvm/vmx.c | 17 +++++++++++++++++ > 1 files changed, 17 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 29e8f42..6056d88 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -1002,6 +1002,15 @@ static void __loaded_vmcs_clear(void *arg) > if (per_cpu(current_vmcs, cpu) == loaded_vmcs->vmcs) > per_cpu(current_vmcs, cpu) = NULL; > list_del(&loaded_vmcs->loaded_vmcss_on_cpu_link); > + > + /* > + * we should ensure updating loaded_vmcs->loaded_vmcss_on_cpu_link > + * is before setting loaded_vmcs->vcpu to -1 which is done in > + * loaded_vmcs_init. Otherwise, other cpu can see vcpu = -1 fist > + * then adds the vmcs into percpu list before it is deleted. > + */ > + smp_wmb(); > + Neither loads nor stores are reordered with like operations (see section 8.2.3.2 of intel's volume 3). This behaviour makes the barrier not necessary. However, i agree access to loaded_vmcs is not obviously safe. I can't tell its safe with vmm_exclusive = 0 (where vcpu->cpu can change at any time). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
