Re: [Qemu-devel] [PATCH] xen-hvm: ignore background I/O sections

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/05/2016 18:18, Paul Durrant wrote:
> Since Xen will correctly handle accesses to unimplemented I/O ports (by
> returning all 1's for reads and ignoring writes) there is no need for
> QEMU to register backgroud I/O sections.
> 
> This patch therefore adds checks to xen_io_add/del so that sections with
> memory-region ops pointing at 'unassigned_io_ops' are ignored.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Anthony Perard <anthony.perard@citrix.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  xen-hvm.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/xen-hvm.c b/xen-hvm.c
> index 039680a..8ab44f0 100644
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -510,8 +510,12 @@ static void xen_io_add(MemoryListener *listener,
>                         MemoryRegionSection *section)
>  {
>      XenIOState *state = container_of(listener, XenIOState, io_listener);
> +    MemoryRegion *mr = section->mr;
>  
> -    memory_region_ref(section->mr);
> +    if (mr->ops == &unassigned_io_ops)
> +        return;

Missing braces, same in xen_io_del.  Otherwise looks ok.

Paolo

> +    memory_region_ref(mr);
>  
>      xen_map_io_section(xen_xc, xen_domid, state->ioservid, section);
>  }
> @@ -520,10 +524,14 @@ static void xen_io_del(MemoryListener *listener,
>                         MemoryRegionSection *section)
>  {
>      XenIOState *state = container_of(listener, XenIOState, io_listener);
> +    MemoryRegion *mr = section->mr;
> +
> +    if (mr->ops == &unassigned_io_ops)
> +        return;
>  
>      xen_unmap_io_section(xen_xc, xen_domid, state->ioservid, section);
>  
> -    memory_region_unref(section->mr);
> +    memory_region_unref(mr);
>  }
>  
>  static void xen_device_realize(DeviceListener *listener,
>