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/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>
---
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
On 10/27/23 20:21, 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/[email protected]
> Signed-off-by: Sean Christopherson <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Paolo
On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <[email protected]> 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/[email protected]
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
Reviewed-by: Fuad Tabba <[email protected]>
Tested-by: Fuad Tabba <[email protected]>
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
>