Re: [Qemu-devel] issues of region cache and iommu reset

[Jason Wang]

On 2017年03月29日 16:45, Cornelia Huck wrote:
> On Wed, 29 Mar 2017 10:09:10 +0200
> Paolo Bonzini <address@hidden> wrote:
>
> > On 29/03/2017 10:00, Jason Wang wrote:
> > > 1) vtd was reset first
> > >
> > > 2) during the reset of virtio-net-pci #1, deletion of msix subregion
> > > will cause a commit of all memory listeners
> > >
> > > 3) virito-net-pci #2's region cache will be update, but since vtd has
> > > already been reset, it can't get a valid mappings here
> > >
> > > Any ideas on how to fix this? Need region cache be aware of IOMMU/IOTLB
> > > state in this case? Or can we simply reset IOMMU as the last one?
> > Something like this?
> >
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 03592c5..73e69ac 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -176,6 +176,10 @@ err_used:
> >       address_space_cache_destroy(&new->desc);
> >   err_desc:
> >       g_free(new);
> > +    atomic_rcu_set(&vq->vring.caches, NULL);
> > +    if (old) {
> > +        call_rcu(old, virtio_free_region_cache, rcu);
> > +    }
> Maybe I'm just confused here, but isn't ->broken enough to prevent
> further accesses?

Looks not (e.g virtio_queue_update_used_idx() that was called by vhost). 
We only have pfn check for all helpers now.

> And a reset will unset both ->broken and the caches
> anyway? What am I missing?

Yes, but is it good to store invalid or even wrong mappings in the cache?

Thanks

> >   }
> >
> >   /* virt queue functions */
> >
> > Paolo