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Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Fri, 27 Oct 2023 11:21:46 -0700
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Subject: [PATCH v13 04/35] KVM: WARN if there are dangling MMU invalidations
 at VM destruction
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>, Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
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        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Sean Christopherson <seanjc@google.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kvmarm@lists.linux.dev, linux-mips@vger.kernel.org,
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        Xiaoyao Li <xiaoyao.li@intel.com>,
        Xu Yilun <yilun.xu@intel.com>,
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        Fuad Tabba <tabba@google.com>,
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        Anish Moorthy <amoorthy@google.com>,
        David Matlack <dmatlack@google.com>,
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        Isaku Yamahata <isaku.yamahata@intel.com>,
        "=?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?=" <mic@digikod.net>,
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        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
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        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
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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>
---
 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