Re: [PATCH] accel/kvm: add PIO ioeventfds only in case kvm_eventfds_allowed is true

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Sat, Oct 17, 2020 at 02:01:01PM -0700, Elena Afanasova wrote:
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Elena Afanasova <eafanasova@gmail.com>
> ---
>  accel/kvm/kvm-all.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Additional information for the commit description:

  MMIO eventfd_add/del are only registered when kvm_eventfds_allowed is
  true but for PIO they are registered unconditionally. This is a bug
  because kvm.ko ioeventfd should not be used if kvm_eventfds_allowed is
  false.

  This issue is a latent bug because ioeventfd is usually available when
  KVM is enabled.

> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 9ef5daf4c5..baaa54249d 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2239,8 +2239,10 @@ static int kvm_init(MachineState *ms)
>  
>      kvm_memory_listener_register(s, &s->memory_listener,
>                                   &address_space_memory, 0);
> -    memory_listener_register(&kvm_io_listener,
> -                             &address_space_io);
> +    if (kvm_eventfds_allowed) {
> +        memory_listener_register(&kvm_io_listener,
> +                                 &address_space_io);
> +    }
>      memory_listener_register(&kvm_coalesced_pio_listener,
>                               &address_space_io);
>  
> -- 
> 2.25.1
> 

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