On Fri, Nov 4, 2016 at 2:48 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
>
> On 03/11/2016 23:26, Ignacio Alvarado wrote:
>> The risk would still be present since fire_user_return_notifiers could
>> potentially run at any time and kvm_on_user return could be called
>> from drop_user_return_notifiers either from the kvm_put_kvm path or
>> the kvm_arch_exit path.
>
> So, do the unregistration
>
> locals->registered = false;
> user_return_notifier_unregister(urn);
>
> first in kvm_on_user_return? Nothing else needs to run with IRQs
> disabled, and doing it first prevents reentering the code from
> kvm_arch_hardware_disable.
>
Will do.
> Paolo
>
>> Regards
>>
>> On Wed, Nov 2, 2016 at 10:25 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>>
>>>
>>> On 22/10/2016 00:08, Ignacio Alvarado wrote:
>>>> Function user_notifier_unregister should be called only once for each
>>>> registered user notifier.
>>>>
>>>> Function kvm_arch_hardware_disable can be executed from an IPI context
>>>> which could cause a race condition with a VCPU returning to user mode
>>>> and attempting to unregister the notifier.
>>>>
>>>> Signed-off-by: Ignacio Alvarado <ikalvarado@xxxxxxxxxx>
>>>
>>> Should drop_user_return_notifiers instead be moved to kvm_arch_exit?
>>>
>>> Thanks,
>>>
>>> Paolo
>>>
>>>> ---
>>>> arch/x86/kvm/x86.c | 10 ++++++++++
>>>> 1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index e375235..51f87f0 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -210,7 +210,15 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
>>>> struct kvm_shared_msrs *locals
>>>> = container_of(urn, struct kvm_shared_msrs, urn);
>>>> struct kvm_shared_msr_values *values;
>>>> + unsigned long flags;
>>>>
>>>> + /*
>>>> + * Disabling irqs at this point since the following code could be
>>>> + * interrupted and executed through kvm_arch_hardware_disable()
>>>> + */
>>>> + local_irq_save(flags);
>>>> + if (!locals->registered)
>>>> + goto out;
>>>> for (slot = 0; slot < shared_msrs_global.nr; ++slot) {
>>>> values = &locals->values[slot];
>>>> if (values->host != values->curr) {
>>>> @@ -220,6 +228,8 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
>>>> }
>>>> locals->registered = false;
>>>> user_return_notifier_unregister(urn);
>>>> +out:
>>>> + local_irq_restore(flags);
>>>> }
>>>>
>>>> static void shared_msr_update(unsigned slot, u32 msr)
>>>>
>>
>>
>>
--
Ignacio Alvarado
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