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

[Linu Cherian]

On Fri Oct 06, 2017 at 09:24:20AM +0200, Auger Eric wrote:
> Hi Bharat,
> 
> On 06/10/2017 05:46, Bharat Bhushan wrote:
> > 
> > 
> >>>> 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?
> 
> On my side I used an i350T2 device (igb) to reproduce the issue.

Myself used a Thunderx NIC which is an on chip PCI device.


-- 
Linu cherian