On 04/11/2016 20:15, 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>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> Changelog since v1:
> - Move unregistration to the beginning of kvm_on_user_return
>
> arch/x86/kvm/x86.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e375235..952e19d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -210,7 +210,18 @@ 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) {
> + locals->registered = false;
> + user_return_notifier_unregister(urn);
> + }
> + local_irq_restore(flags);
> for (slot = 0; slot < shared_msrs_global.nr; ++slot) {
> values = &locals->values[slot];
> if (values->host != values->curr) {
> @@ -218,8 +229,6 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
> values->curr = values->host;
> }
> }
> - locals->registered = false;
> - user_return_notifier_unregister(urn);
> }
>
> static void shared_msr_update(unsigned slot, u32 msr)
>
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