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KVM: WARN if there are dangling MMU invalidations at VM destruction

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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@linux.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Message-Id: <20231027182217.3615211-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-10-27 11:21:46 -07:00 committed by Paolo Bonzini
parent 8569992d64
commit d497a0fab8
1 changed files with 8 additions and 1 deletions
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9
virt/kvm/kvm_main.c
View file

@ -1358,9 +1358,16 @@ 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