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Message-ID: <20230921203331.3746712-5-seanjc@google.com>
Date: Thu, 21 Sep 2023 13:33:21 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Michael Roth <michael.roth@....com>,
Binbin Wu <binbin.wu@...ux.intel.com>
Subject: [PATCH 04/13] KVM: WARN if there are danging MMU invalidations at VM destruction
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@...gle.com>
---
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
+ * 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
--
2.42.0.515.g380fc7ccd1-goog
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