Date:   Thu, 24 Oct 2019 16:03:25 -0700
In-Reply-To: <20191024230327.140935-1-jmattson@google.com>
Message-Id: <20191024230327.140935-2-jmattson@google.com>
Mime-Version: 1.0
References: <20191024230327.140935-1-jmattson@google.com>
Subject: [PATCH v3 1/3] kvm: Don't clear reference count on kvm_create_vm()
 error path
From:   Jim Mattson <jmattson@google.com>
To:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        John Sperbeck <jsperbeck@google.com>,
        Junaid Shahid <junaids@google.com>
Cc:     Jim Mattson <jmattson@google.com>
Content-Type: text/plain; charset="UTF-8"
Sender: kvm-owner@vger.kernel.org
Precedence: bulk

Defer setting the reference count, kvm->users_count, until the VM is
guaranteed to be created, so that the reference count need not be
cleared on the error path.

Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Junaid Shahid <junaids@google.com>
---
 virt/kvm/kvm_main.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fd68fbe0a75d2..525e0dbc623f9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -640,7 +640,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
 	mutex_init(&kvm->lock);
 	mutex_init(&kvm->irq_lock);
 	mutex_init(&kvm->slots_lock);
-	refcount_set(&kvm->users_count, 1);
 	INIT_LIST_HEAD(&kvm->devices);
 
 	r = kvm_arch_init_vm(kvm, type);
@@ -682,6 +681,12 @@ static struct kvm *kvm_create_vm(unsigned long type)
 	if (r)
 		goto out_err;
 
+	/*
+	 * kvm_get_kvm() isn't legal while the vm is being created
+	 * (e.g. in kvm_arch_init_vm).
+	 */
+	refcount_set(&kvm->users_count, 1);
+
 	mutex_lock(&kvm_lock);
 	list_add(&kvm->vm_list, &vm_list);
 	mutex_unlock(&kvm_lock);
@@ -697,7 +702,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
 out_err_no_srcu:
 	hardware_disable_all();
 out_err_no_disable:
-	refcount_set(&kvm->users_count, 0);
 	for (i = 0; i < KVM_NR_BUSES; i++)
 		kfree(kvm_get_bus(kvm, i));
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
-- 
2.24.0.rc0.303.g954a862665-goog