Re: [Qemu-devel] [PATCH for-2.11] vfio: Fix vfio-kvm group registration

[Liu, Yi L]

On Tue, Dec 05, 2017 at 02:09:07PM -0700, Alex Williamson wrote:
> Commit 8c37faa475f3 ("vfio-pci, ppc64/spapr: Reorder group-to-container
> attaching") moved registration of groups with the vfio-kvm device from
> vfio_get_group() to vfio_connect_container(), but it missed the case
> where a group is attached to an existing container and takes an early
> exit.  Perhaps this is a less common case on ppc64/spapr, but on x86
> (without viommu) all groups are connected to the same container and
> thus only the first group gets registered with the vfio-kvm device.
> This becomes a problem if we then hot-unplug the devices associated
> with that first group and we end up with KVM being misinformed about
> any vfio connections that might remain.  Fix by including the call to
> vfio_kvm_device_add_group() in this early exit path.
> 
> Fixes: 8c37faa475f3 ("vfio-pci, ppc64/spapr: Reorder group-to-container 
> attaching")
> Cc: address@hidden # qemu-2.10+
> Signed-off-by: Alex Williamson <address@hidden>
> ---
> 
> This bug also existed in QEMU 2.10, but I think the fix is sufficiently
> obvious (famous last words) to propose for 2.11 at this late date.  If
> the first group is hot unplugged then KVM may revert to code emulation
> that assumes no non-coherent DMA is present on some systems.  Also for
> KVMGT, if the vGPU is not the first device registered, then the
> notifier to enable linkages to KVM would not be called.  Please review.
> Thanks,

Alex, for x86, I suppose it doesn't exist in the case which viommu is exposed
to guest?

Regards,
Yi L
> 
>  hw/vfio/common.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 7b2924c0ef19..7007878e345e 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -968,6 +968,7 @@ static int vfio_connect_container(VFIOGroup *group, 
> AddressSpace *as,
>          if (!ioctl(group->fd, VFIO_GROUP_SET_CONTAINER, &container->fd)) {
>              group->container = container;
>              QLIST_INSERT_HEAD(&container->group_list, group, container_next);
> +            vfio_kvm_device_add_group(group);
>              return 0;
>          }
>      }
> 
>