Re: [PATCH 2/3] vdpa: Add vhost_vdpa_section_end

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

On Tue, Oct 05, 2021 at 10:01:30AM +0200, Eugenio Pérez wrote:
> Abstract this operation, that will be reused when validating the region
> against the iova range that the device supports.
> 
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>

Note that as defined end is actually 1 byte beyond end of section.
As such it can e.g. overflow if cast to u64.
So be careful to use int128 ops with it.
Also - document?

> ---
>  hw/virtio/vhost-vdpa.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index ea1aa71ad8..a1de6c7c9c 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -24,6 +24,15 @@
>  #include "trace.h"
>  #include "qemu-common.h"
>  
> +static Int128 vhost_vdpa_section_end(const MemoryRegionSection *section)
> +{
> +    Int128 llend = int128_make64(section->offset_within_address_space);
> +    llend = int128_add(llend, section->size);
> +    llend = int128_and(llend, int128_exts64(TARGET_PAGE_MASK));
> +
> +    return llend;
> +}
> +
>  static bool vhost_vdpa_listener_skipped_section(MemoryRegionSection *section)
>  {
>      return (!memory_region_is_ram(section->mr) &&
> @@ -160,10 +169,7 @@ static void vhost_vdpa_listener_region_add(MemoryListener *listener,
>      }
>  
>      iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
> -    llend = int128_make64(section->offset_within_address_space);
> -    llend = int128_add(llend, section->size);
> -    llend = int128_and(llend, int128_exts64(TARGET_PAGE_MASK));
> -
> +    llend = vhost_vdpa_section_end(section);
>      if (int128_ge(int128_make64(iova), llend)) {
>          return;
>      }
> @@ -221,9 +227,7 @@ static void vhost_vdpa_listener_region_del(MemoryListener *listener,
>      }
>  
>      iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
> -    llend = int128_make64(section->offset_within_address_space);
> -    llend = int128_add(llend, section->size);
> -    llend = int128_and(llend, int128_exts64(TARGET_PAGE_MASK));
> +    llend = vhost_vdpa_section_end(section);
>  
>      trace_vhost_vdpa_listener_region_del(v, iova, int128_get64(llend));
>  
> -- 
> 2.27.0