Re: [PATCH] KVM: fix spin_lock_init order on x86

From: Paolo Bonzini
Date: Mon Mar 21 2016 - 11:19:26 EST




On 21/03/2016 15:47, Eric Dumazet wrote:
> On Mon, 2016-03-21 at 10:24 +0100, Paolo Bonzini wrote:
>> kvm_arch_init_vm is now using mmu_lock, causing lockdep to
>> complain:
> ...
>>
>> Reported-by: Borislav Petkov <bp@xxxxxxxxx>
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> virt/kvm/kvm_main.c | 20 ++++++++++----------
>> 1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 7ba1d10ffed2..cb45b86a1c48 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -536,6 +536,16 @@ static struct kvm *kvm_create_vm(unsigned long type)
>> if (!kvm)
>> return ERR_PTR(-ENOMEM);
>>
>> + spin_lock_init(&kvm->mmu_lock);
>> + kvm->mm = current->mm;
>> + atomic_inc(&kvm->mm->mm_count);
>
> current->mm->mm_count is incremented here.
>
>> + 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_no_disable;
>
>
> But out_err_no_disable wont decrement it in case of an error.
>
> This is not clear to me where the cleanup is done ?

Indeed, a slightly more complex patch is necessary. Will try again,
this time not doing this as the first thing in the morning.

Paolo

>> @@ -568,16 +578,6 @@ 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;
>
>