Re: [Qemu-devel] [PATCH] vhost: Allow abutting regions

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Mar 23, 2018 at 12:46:37PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> My rework of section adding combines overlapping or abutting regions,
> but checks they're actually the same underlying RAM block.
> Fix the case where two blocks abut but don't overlap; that new region
> should get added (but not combined), but my previous patch was disallowing it.
> 
> Fixes: c1ece84e7c9
> 
> Reported-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

I prefer adjacent and not abutting.

> ---
>  hw/virtio/vhost.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 250f886acb..fc9062a89f 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -595,10 +595,15 @@ static void vhost_region_add_section(struct vhost_dev *dev,
>                                          prev_sec->offset_within_address_space,
>                                          prev_sec->offset_within_region);
>              } else {
> -                error_report("%s: Overlapping but not coherent sections "
> -                             "at %"PRIx64,
> -                             __func__, mrs_gpa);
> -                return;
> +                /* abutting regions are fine, but overlapping ones with
> +                 * different blocks/offsets shouldn't happen
> +                 */
> +                if (mrs_gpa != prev_gpa_end + 1) {
> +                    error_report("%s: Overlapping but not coherent sections "
> +                                 "at %"PRIx64,
> +                                 __func__, mrs_gpa);
> +                    return;
> +                }
>              }
>          }
>      }
> -- 
> 2.14.3