Patch "KVM: fix spin_lock_init order on x86" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

KVM: fix spin_lock_init order on x86

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-fix-spin_lock_init-order-on-x86.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paolo Bonzini <[email protected]>
Date: Mon, 21 Mar 2016 10:15:25 +0100
Subject: KVM: fix spin_lock_init order on x86

From: Paolo Bonzini <[email protected]>

commit e9ad4ec8379ad1ba6f68b8ca1c26b50b5ae0a327 upstream.

Moving the initialization earlier is needed in 4.6 because kvm_arch_init_vm is now using mmu_lock, causing lockdep to complain:

[  284.440294] INFO: trying to register non-static key.
[  284.445259] the code is fine but needs lockdep annotation.
[  284.450736] turning off the locking correctness validator.
...
[  284.528318]  [<ffffffff810aecc3>] lock_acquire+0xd3/0x240
[  284.533733]  [<ffffffffa0305aa0>] ? kvm_page_track_register_notifier+0x20/0x60 [kvm]
[  284.541467]  [<ffffffff81715581>] _raw_spin_lock+0x41/0x80
[  284.546960]  [<ffffffffa0305aa0>] ? kvm_page_track_register_notifier+0x20/0x60 [kvm]
[  284.554707]  [<ffffffffa0305aa0>] kvm_page_track_register_notifier+0x20/0x60 [kvm]
[  284.562281]  [<ffffffffa02ece70>] kvm_mmu_init_vm+0x20/0x30 [kvm]
[  284.568381]  [<ffffffffa02dbf7a>] kvm_arch_init_vm+0x1ea/0x200 [kvm]
[  284.574740]  [<ffffffffa02bff3f>] kvm_dev_ioctl+0xbf/0x4d0 [kvm]

However, it also helps fixing a preexisting problem, which is why this patch is also good for stable kernels: kvm_create_vm was incrementing current->mm->mm_count but not decrementing it at the out_err label (in case kvm_init_mmu_notifier failed). The new initialization order makes it possible to add the required mmdrop without adding a new error label.

---
 virt/kvm/kvm_main.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

@@ -454,6 +454,16 @@ static struct kvm *kvm_create_vm(unsigne
 	if (!kvm)
 		return ERR_PTR(-ENOMEM);
 
+	spin_lock_init(&kvm->mmu_lock);
+	atomic_inc(&current->mm->mm_count);
+	kvm->mm = current->mm;
+	kvm_eventfd_init(kvm);
+	mutex_init(&kvm->lock);
+	mutex_init(&kvm->irq_lock);
+	mutex_init(&kvm->slots_lock);
+	atomic_set(&kvm->users_count, 1);
+	INIT_LIST_HEAD(&kvm->devices);
+
 	r = kvm_arch_init_vm(kvm, type);
 	if (r)
 		goto out_err_nodisable;

@@ -483,16 +493,6 @@ static struct kvm *kvm_create_vm(unsigne
 			goto out_err;
 	}
 
-	spin_lock_init(&kvm->mmu_lock);
-	kvm->mm = current->mm;
-	atomic_inc(&kvm->mm->mm_count);
-	kvm_eventfd_init(kvm);
-	mutex_init(&kvm->lock);
-	mutex_init(&kvm->irq_lock);
-	mutex_init(&kvm->slots_lock);
-	atomic_set(&kvm->users_count, 1);
-	INIT_LIST_HEAD(&kvm->devices);
-
 	r = kvm_init_mmu_notifier(kvm);
 	if (r)
 		goto out_err;

@@ -512,6 +512,7 @@ out_err_nodisable:
 		kfree(kvm->buses[i]);
 	kfree(kvm->memslots);
 	kvm_arch_free_vm(kvm);
+	mmdrop(current->mm);
 	return ERR_PTR(r);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/kvm-i8254-change-pit-discard-tick-policy.patch queue-3.14/kvm-fix-spin_lock_init-order-on-x86.patch queue-3.14/kvm-vmx-avoid-guest-hang-on-invalid-invept-instruction.patch