Re: [Qemu-arm] [Qemu-devel] [PATCH v4 0/5] virtio-iommu: VFIO integration

[Bharat Bhushan]

> >> Thanks
> >>
> >> Eric
> >>>
> >>> However you should be allowed to map 1 sg element of 5 pages and
> >>> then notify the host about this event I think. Still looking at the 
> >>> code...
> >>>
> >>> I still can't reproduce the issue at the moment. What kind of device
> >>> are you assigning?
> >>>
> >>> Thanks
> >>>
> >>> Eric
> >>>>
> >>>> Atleast vfio_get_vaddr called from vfio_iommu_map_notify in Qemu
> >>>> expects the map size to be a power of 2.
> >
> > Actually I missed the most important here ;-)
> >>>>
> >>>>  if (len & iotlb->addr_mask) {
> > This check looks suspiscious to me. In our case the len is not
> > modified by the previous translation and it fails, I don't see why. It
> > should be valid to be able to notify 5 granules.
> 
> So after discussion with Alex, looks the way we notify the host currently is
> wrong. we set the addr_mask to the mapping/unmapping size
> -1 whereas this should be a page mask instead (granule size or block size?).
> So if the guest maps 5 x 4kB pages we should send 5 notifications for each
> page and not a single one. It is unclear to me if we can notify with
> hugepage/block page size mask. Peter may confirm/infirm this. in vsmmuv3
> code I notify by granule or block size.
> 
> Bharat, please can you add this to your TODO list?
> 
> Linu, thanks a lot for the time you spent debugging this issue.
> Curiously on my side, it is really seldom hit but it is ...

Thanks Linu and Eric, I added this to my todo list.
While I am still not able to reproduce the issue.  I tried with e1000 and now 
try with ixgbe device. May I know which device can be used to reproduce this 
issue?

Thanks
-Bharat

> 
> Thanks!
> 
> Eric
> >
> > Thanks
> >
> > Eric
> >>>>         error_report("iommu has granularity incompatible with target 
> >>>> AS");
> >>>>         return false;
> >>>>     }
> >>>>
> >>>> Just trying to understand how this is not hitting in your case.
> >>>>
> >>>>
> >>>
> >>
> >