On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@xxxxxxxxxx> 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> > --- Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx> Tested-by: Fuad Tabba <tabba@xxxxxxxxxx> Cheers, /fuad > 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 1a577a25de47..4dba682586ee 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -1356,9 +1356,16 @@ 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 its MMU > + * notifier between a start() and end(), then there shouldn't be any > + * in-progress invalidations. > */ > WARN_ON(rcuwait_active(&kvm->mn_memslots_update_rcuwait)); > - kvm->mn_active_invalidate_count = 0; > + if (kvm->mn_active_invalidate_count) > + kvm->mn_active_invalidate_count = 0; > + else > + WARN_ON(kvm->mmu_invalidate_in_progress); > #else > kvm_flush_shadow_all(kvm); > #endif > -- > 2.42.0.820.g83a721a137-goog >
