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Subject[PATCH 3.13.y-ckt 67/97] KVM: fix spin_lock_init order on x86
Date
3.13.11-ckt38 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Paolo Bonzini <pbonzini@redhat.com>

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.

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
virt/kvm/kvm_main.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 634048e..afcaf33 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -450,6 +450,16 @@ static struct kvm *kvm_create_vm(unsigned long type)
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;
@@ -486,16 +496,6 @@ static struct kvm *kvm_create_vm(unsigned long type)
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;
@@ -515,6 +515,7 @@ out_err_nodisable:
kfree(kvm->buses[i]);
kfree(kvm->memslots);
kvm_arch_free_vm(kvm);
+ mmdrop(current->mm);
return ERR_PTR(r);
}

--
2.7.4
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