On Wed, Sep 27, 2023, Binbin Wu wrote: > > > On 9/22/2023 4:33 AM, Sean Christopherson wrote: > > Add an assertion that there are no in-progress MMU invalidations when a > > VM is being destroyed, with the exception of the scenario where KVM > > unregisters its MMU notifier between an .invalidate_range_start() call and > > the corresponding .invalidate_range_end(). > > > > KVM can't detect unpaired calls from the mmu_notifier due to the above > > exception waiver, but the assertion can detect KVM bugs, e.g. such as the > > bug that *almost* escaped initial guest_memfd development. > > > > Link: https://lore.kernel.org/all/e397d30c-c6af-e68f-d18e-b4e3739c5389@xxxxxxxxxxxxxxx > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > --- > > virt/kvm/kvm_main.c | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 54480655bcce..277afeedd670 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -1381,9 +1381,16 @@ static void kvm_destroy_vm(struct kvm *kvm) > > * No threads can be waiting in kvm_swap_active_memslots() as the > > * last reference on KVM has been dropped, but freeing > > * memslots would deadlock without this manual intervention. > > + * > > + * If the count isn't unbalanced, i.e. KVM did NOT unregister between > Nit: Readers can get it according to the code context, but is it better to > add "MMU notifier" to tell what to "unregister" to make the comment easier > to understand? Agreed, I'll add that when applying.
