[PATCH] KVM: Initialize kvm before registering the mmu notifier

[PATCH] KVM: Initialize kvm before registering the mmu notifier

[Mike Waychison]

It doesn't make sense to ever see a half-initialized kvm structure on
mmu notifier callbacks.  Previously, 85722cda changed the ordering to
ensure that the mmu_lock was initialized before mmu notifier
registration, but there is still a race where the mmu notifier could
come in and try accessing other portions of struct kvm before they are
intialized.

Solve this by moving the mmu notifier registration to occur after the
structure is completely initialized.

Google-Bug-Id: 452199
Signed-off-by: Mike Waychison <mikew@google.com>

---
Applies to Linus' tree.
---
 virt/kvm/kvm_main.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 22cdb96..ba781f4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -467,12 +467,8 @@ static struct kvm *kvm_create_vm(void)
 		if (!kvm->buses[i])
 			goto out_err;
 	}
-	spin_lock_init(&kvm->mmu_lock);
-
-	r = kvm_init_mmu_notifier(kvm);
-	if (r)
-		goto out_err;
 
+	spin_lock_init(&kvm->mmu_lock);
 	kvm->mm = current->mm;
 	atomic_inc(&kvm->mm->mm_count);
 	kvm_eventfd_init(kvm);
@@ -480,6 +476,11 @@ static struct kvm *kvm_create_vm(void)
 	mutex_init(&kvm->irq_lock);
 	mutex_init(&kvm->slots_lock);
 	atomic_set(&kvm->users_count, 1);
+
+	r = kvm_init_mmu_notifier(kvm);
+	if (r)
+		goto out_err;
+
 	raw_spin_lock(&kvm_lock);
 	list_add(&kvm->vm_list, &vm_list);
 	raw_spin_unlock(&kvm_lock);
-- 
1.7.3.1

Re: [PATCH] KVM: Initialize kvm before registering the mmu notifier

[Avi Kivity]

On 06/03/2011 11:04 PM, Mike Waychison wrote:
> It doesn't make sense to ever see a half-initialized kvm structure on
> mmu notifier callbacks.  Previously, 85722cda changed the ordering to
> ensure that the mmu_lock was initialized before mmu notifier
> registration, but there is still a race where the mmu notifier could
> come in and try accessing other portions of struct kvm before they are
> intialized.
>
> Solve this by moving the mmu notifier registration to occur after the
> structure is completely initialized.

Thanks, applied, and queued for 3.0.

-- 
error compiling committee.c: too many arguments to function