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)
>
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