Re: [RFC][PATCH 1/5] [PATCH 1/5] kvm: register in task_struct

[Fengguang Wu]

On Tue, Sep 04, 2018 at 08:37:03AM +0200, Nikita Leshenko wrote:
> On 4 Sep 2018, at 2:46, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
> > Here it goes:
> >
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 99ce070e7dcb..27c5446f3deb 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -27,6 +27,7 @@ typedef int vm_fault_t;
> > struct address_space;
> > struct mem_cgroup;
> > struct hmm;
> > +struct kvm;
> > /*
> > * Each physical page in the system has a struct page associated with
> > @@ -489,10 +490,19 @@ struct mm_struct {
> > 	/* HMM needs to track a few things per mm */
> > 	struct hmm *hmm;
> > #endif
> > +#if IS_ENABLED(CONFIG_KVM)
> > +	struct kvm *kvm;
> > +#endif
> > } __randomize_layout;
> > extern struct mm_struct init_mm;
> > +#if IS_ENABLED(CONFIG_KVM)
> > +static inline struct kvm *mm_kvm(struct mm_struct *mm) { return mm->kvm; }
> > +#else
> > +static inline struct kvm *mm_kvm(struct mm_struct *mm) { return NULL; }
> > +#endif
> > +
> > static inline void mm_init_cpumask(struct mm_struct *mm)
> > {
> > #ifdef CONFIG_CPUMASK_OFFSTACK
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 0c483720de8d..dca6156a7b35 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -3892,7 +3892,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
> > 	if (type == KVM_EVENT_CREATE_VM) {
> > 		add_uevent_var(env, "EVENT=create");
> > 		kvm->userspace_pid = task_pid_nr(current);
> > -		current->kvm = kvm;
> > +		current->mm->kvm = kvm;
> I think you also need to reset kvm to NULL once the VM is
> destroyed, otherwise it would point to dangling memory.

Good point! Here is the incremental patch:

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3894,6 +3894,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
               kvm->userspace_pid = task_pid_nr(current);
               current->mm->kvm = kvm;
       } else if (type == KVM_EVENT_DESTROY_VM) {
+               current->mm->kvm = NULL;
               add_uevent_var(env, "EVENT=destroy");
       }
       add_uevent_var(env, "PID=%d", kvm->userspace_pid);

Thanks,
Fengguang