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Re: [Qemu-devel] [PATCH for-2.11] vfio: Fix vfio-kvm group registration
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH for-2.11] vfio: Fix vfio-kvm group registration |
Date: |
Tue, 5 Dec 2017 20:12:58 -0700 |
On Wed, 6 Dec 2017 10:44:43 +0800
"Liu, Yi L" <address@hidden> wrote:
> 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?
With viommu, I believe each group would be in its own AddressSpace and
therefore get a separate container, so I don't think it'd be an issue.
It's only subsequent groups added to the same container which are
missed. Thanks,
Alex
> > 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;
> > }
> > }
> >
> >