Re: [PATCH v6 05/12] vfio: Support for RamDiscardMgr in the !vIOMMU case

[David Hildenbrand]

On 22.02.21 14:20, Paolo Bonzini wrote:
> On 22/02/21 12:57, David Hildenbrand wrote:
> > +static int vfio_sync_ram_discard_listener_dirty_bitmap(VFIOContainer 
> > *container,
> > +                                                   MemoryRegionSection 
> > *section)
> > +{
> > +    RamDiscardMgr *rdm = memory_region_get_ram_discard_mgr(section->mr);
> > +    RamDiscardMgrClass *rdmc = RAM_DISCARD_MGR_GET_CLASS(rdm);
> > +    VFIORamDiscardListener tmp_vrdl, *vrdl = NULL;
> > +
> > +    QLIST_FOREACH(vrdl, &container->vrdl_list, next) {
> > +        if (vrdl->mr == section->mr &&
> > +            vrdl->offset_within_region == section->offset_within_region) {
> > +            break;
> > +        }
> > +    }
> > +
> > +    if (!vrdl) {
> > +        hw_error("vfio: Trying to sync missing RAM discard listener");
> > +    }
> > +
> > +    tmp_vrdl = *vrdl;
> > +    ram_discard_listener_init(&tmp_vrdl.listener,
> > +                              vfio_ram_discard_notify_dirty_bitmap, NULL, 
> > NULL);
> > +    return rdmc->replay_populated(rdm, section->mr, &tmp_vrdl.listener);
> > +}
> > +
>
> Can you explain why this is related to the sync_dirty_bitmap call?  This
> needs a comment in vfio_sync_dirty_bitmap.

We can only synchronize the parts that actually got mapped via VFIO. So 
I have to walk all parts that are populated (and thus, were mapped via 
VFIO). This is similar to the IOMMU notifier handling.

> Also, why can't you just pass vrdl to the call?

I have to modify the callbacks. Similarly done for 
memory_region_iommu_replay().

--
Thanks,

David / dhildenb