RE: [RFC 00/18] vfio: Adopt iommufd

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Eric Auger [mailto:eric.auger@redhat.com]
> Sent: 26 April 2022 12:45
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>; Yi
> Liu <yi.l.liu@intel.com>; alex.williamson@redhat.com; cohuck@redhat.com;
> qemu-devel@nongnu.org
> Cc: david@gibson.dropbear.id.au; thuth@redhat.com; farman@linux.ibm.com;
> mjrosato@linux.ibm.com; akrowiak@linux.ibm.com; pasic@linux.ibm.com;
> jjherne@linux.ibm.com; jasowang@redhat.com; kvm@vger.kernel.org;
> jgg@nvidia.com; nicolinc@nvidia.com; eric.auger.pro@gmail.com;
> kevin.tian@intel.com; chao.p.peng@intel.com; yi.y.sun@intel.com;
> peterx@redhat.com; Zhangfei Gao <zhangfei.gao@linaro.org>
> Subject: Re: [RFC 00/18] vfio: Adopt iommufd

[...]
 
> >>
> https://lore.kernel.org/kvm/0-v1-e79cd8d168e8+6-iommufd_jgg@nvidia.com
> >> /
> >> [2] https://github.com/luxis1999/iommufd/tree/iommufd-v5.17-rc6
> >> [3] https://github.com/luxis1999/qemu/tree/qemu-for-5.17-rc6-vm-rfcv1
> > Hi,
> >
> > I had a go with the above branches on our ARM64 platform trying to
> pass-through
> > a VF dev, but Qemu reports an error as below,
> >
> > [    0.444728] hisi_sec2 0000:00:01.0: enabling device (0000 -> 0002)
> > qemu-system-aarch64-iommufd: IOMMU_IOAS_MAP failed: Bad address
> > qemu-system-aarch64-iommufd: vfio_container_dma_map(0xaaaafeb40ce0,
> 0x8000000000, 0x10000, 0xffffb40ef000) = -14 (Bad address)
> >
> > I think this happens for the dev BAR addr range. I haven't debugged the
> kernel
> > yet to see where it actually reports that.
> Does it prevent your assigned device from working? I have such errors
> too but this is a known issue. This is due to the fact P2P DMA is not
> supported yet.
> 

Yes, the basic tests all good so far. I am still not very clear how it works if
the map() fails though. It looks like it fails in,

iommufd_ioas_map()
  iopt_map_user_pages()
   iopt_map_pages()
   ..
     pfn_reader_pin_pages()

So does it mean it just works because the page is resident()?

Thanks,
Shameer