From 42a90008f890afc41837dfeec1f0b1e7bcecf94a Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Wed, 11 Jan 2023 18:06:50 +0000
Subject: [PATCH] KVM: Ensure lockdep knows about kvm->lock vs. vcpu->mutex
ordering rule
Documentation/virt/kvm/locking.rst tells us that kvm->lock is taken outside
vcpu->mutex. But that doesn't actually happen very often; it's only in
some esoteric cases like migration with AMD SEV. This means that lockdep
usually doesn't notice, and doesn't do its job of keeping us honest.
Ensure that lockdep *always* knows about the ordering of these two locks,
by briefly taking vcpu->mutex in kvm_vm_ioctl_create_vcpu() while kvm->lock
is held.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20230111180651.14394-3-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
virt/kvm/kvm_main.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 13e88297f9996..9c60384b5ae0b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3954,6 +3954,13 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
}
mutex_lock(&kvm->lock);
+
+#ifdef CONFIG_LOCKDEP
+ /* Ensure that lockdep knows vcpu->mutex is taken *inside* kvm->lock */
+ mutex_lock(&vcpu->mutex);
+ mutex_unlock(&vcpu->mutex);
+#endif
+
if (kvm_get_vcpu_by_id(kvm, id)) {
r = -EEXIST;
goto unlock_vcpu_destroy;
--
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