Re: [Qemu-devel] [PATCH] vfio: avoid adding same iommu mr for notify

[Alexey Kardashevskiy]

On 15/11/16 11:59, Peter Xu wrote:
> When one IOMMU memory region is splitted into multiple memory sections,


Out of curiosity - when does this happen?


> vfio will register multiple same notifiers to a vIOMMU for the same
> region. That's not sensible. What we need is to register one IOMMU
> notifier for each IOMMU region, not per section.
> 
> Solution is simple - we traverse the container->giommu_list, and skip
> the registration if memory region is already registered.
> 
> To make vfio's region_add() short, vfio_listener_region_add_iommu() is
> introduced.
> 
> Signed-off-by: Peter Xu <address@hidden>
> ---
>  hw/vfio/common.c | 56 
> +++++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 35 insertions(+), 21 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 801578b..5279fd1 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -360,6 +360,40 @@ out:
>      rcu_read_unlock();
>  }
>  
> +static void vfio_listener_region_add_iommu(VFIOContainer *container,
> +                                           MemoryRegionSection *section,
> +                                           hwaddr iova,
> +                                           hwaddr end)
> +{
> +    VFIOGuestIOMMU *giommu;
> +
> +    QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
> +        if (giommu->iommu == section->mr) {
> +            /* We have already registered with this MR, skip */
> +            return;
> +        }
> +    }
> +
> +    trace_vfio_listener_region_add_iommu(iova, end);
> +
> +    /*
> +     * FIXME: For VFIO iommu types which have KVM acceleration to
> +     * avoid bouncing all map/unmaps through qemu this way, this
> +     * would be the right place to wire that up (tell the KVM
> +     * device emulation the VFIO iommu handles to use).
> +     */
> +    giommu = g_malloc0(sizeof(*giommu));
> +    giommu->iommu = section->mr;
> +    giommu->iommu_offset = section->offset_within_address_space -
> +        section->offset_within_region;
> +    giommu->container = container;
> +    giommu->n.notify = vfio_iommu_map_notify;
> +    giommu->n.notifier_flags = IOMMU_NOTIFIER_ALL;
> +    QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
> +    memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
> +    memory_region_iommu_replay(giommu->iommu, &giommu->n, false);
> +}
> +
>  static void vfio_listener_region_add(MemoryListener *listener,
>                                       MemoryRegionSection *section)
>  {
> @@ -439,27 +473,7 @@ static void vfio_listener_region_add(MemoryListener 
> *listener,
>      memory_region_ref(section->mr);
>  
>      if (memory_region_is_iommu(section->mr)) {
> -        VFIOGuestIOMMU *giommu;
> -
> -        trace_vfio_listener_region_add_iommu(iova, end);
> -        /*
> -         * FIXME: For VFIO iommu types which have KVM acceleration to
> -         * avoid bouncing all map/unmaps through qemu this way, this
> -         * would be the right place to wire that up (tell the KVM
> -         * device emulation the VFIO iommu handles to use).
> -         */
> -        giommu = g_malloc0(sizeof(*giommu));
> -        giommu->iommu = section->mr;
> -        giommu->iommu_offset = section->offset_within_address_space -
> -                               section->offset_within_region;
> -        giommu->container = container;
> -        giommu->n.notify = vfio_iommu_map_notify;
> -        giommu->n.notifier_flags = IOMMU_NOTIFIER_ALL;
> -        QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
> -
> -        memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
> -        memory_region_iommu_replay(giommu->iommu, &giommu->n, false);
> -
> +        vfio_listener_region_add_iommu(container, section, iova, end);
>          return;
>      }
>  
> 


-- 
Alexey