linux-kernel - [PATCH 6/6] KVM: Drop hack that "manually" informs lockdep of kvm->lock vs. vcpu->mutex

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Message-ID: <20241009150455.1057573-7-seanjc@google.com>
Date: Wed,  9 Oct 2024 08:04:55 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Will Deacon <will@...nel.org>, Michal Luczaj <mhal@...x.co>, Sean Christopherson <seanjc@...gle.com>, 
	Alexander Potapenko <glider@...gle.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>
Subject: [PATCH 6/6] KVM: Drop hack that "manually" informs lockdep of
 kvm->lock vs. vcpu->mutex

Now that KVM takes vcpu->mutex inside kvm->lock when creating a vCPU, drop
the hack to manually inform lockdep of the kvm->lock => vcpu->mutex
ordering.

This effectively reverts commit 42a90008f890 ("KVM: Ensure lockdep knows
about kvm->lock vs. vcpu->mutex ordering rule").

Cc: Oliver Upton <oliver.upton@...ux.dev>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/kvm_main.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ae216256ee9d..2dd3ff8764da 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4271,12 +4271,6 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long 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;
@@ -4293,7 +4287,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id)
 	 * so that userspace can't invoke vCPU ioctl()s until the vCPU is fully
 	 * visible (per online_vcpus), e.g. so that KVM doesn't get tricked
 	 * into a NULL-pointer dereference because KVM thinks the _current_
-	 * vCPU doesn't exist.
+	 * vCPU doesn't exist.  As a bonus, taking vcpu->mutex ensures lockdep
+	 * knows it's taken *inside* kvm->lock.
 	 */
 	mutex_lock(&vcpu->mutex);
 	kvm_get_kvm(kvm);
-- 
2.47.0.rc0.187.ge670bccf7e-goog