Re: [PATCH v10 10/10] vfio: Don't issue full 2^64 unmap

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 30 Oct 2020 06:25:34 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Thu, Oct 08, 2020 at 03:22:14PM -0600, Alex Williamson wrote:
> > On Thu,  8 Oct 2020 19:15:58 +0200
> > Jean-Philippe Brucker <jean-philippe@linaro.org> wrote:
> >   
> > > IOMMUs may declare memory regions spanning from 0 to UINT64_MAX. When
> > > attempting to deal with such region, vfio_listener_region_del() passes a
> > > size of 2^64 to int128_get64() which throws an assertion failure.  Even
> > > ignoring this, the VFIO_IOMMU_DMA_MAP ioctl cannot handle this size
> > > since the size field is 64-bit. Split the request in two.
> > > 
> > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > > ---
> > > For me this happens when memory_region_iommu_set_page_size_mask()
> > > returns an error because a hotplugged endpoint uses an incompatible page
> > > mask. vfio_connect_container() releases the memory listener which calls
> > > region_del() with the 2^64 IOMMU region. There are probably other ways
> > > to reach this.
> > > ---
> > >  hw/vfio/common.c | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > > 
> > > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > > index e66054b02a7..e90a89c389e 100644
> > > --- a/hw/vfio/common.c
> > > +++ b/hw/vfio/common.c
> > > @@ -797,6 +797,17 @@ static void vfio_listener_region_del(MemoryListener *listener,
> > >      }
> > >  
> > >      if (try_unmap) {
> > > +        if (llsize == int128_2_64()) {
> > > +            /* The unmap ioctl doesn't accept a full 64-bit span. */
> > > +            llsize = int128_rshift(llsize, 1);
> > > +            ret = vfio_dma_unmap(container, iova, int128_get64(llsize));
> > > +            if (ret) {
> > > +                error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
> > > +                             "0x%"HWADDR_PRIx") = %d (%m)",
> > > +                             container, iova, int128_get64(llsize), ret);
> > > +            }
> > > +            iova += int128_get64(llsize);
> > > +        }
> > >          ret = vfio_dma_unmap(container, iova, int128_get64(llsize));
> > >          if (ret) {
> > >              error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "  
> > 
> > We're still susceptible that splitting the range in two could result in
> > unmap calls that attempt to bisect a mapping that spans both ranges.
> > Both unmap calls would fail in that case.  I think we could solve this
> > more completely with a high water marker, but this probably good enough
> > for now.
> > 
> > Acked-by: Alex Williamson <alex.williamson@redhat.com>  
> 
> 
> Are you merging this then?
> If yes
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> 

No, the series is focused on virtio-iommu therefore I assumed you or
Eric would merge it, thus I provided an Ack.  Thanks,

Alex