Re: [PATCH 66/77] virtio: verify that legacy support is not accidentally on

[Cornelia Huck]

On Thu,  3 Sep 2020 15:59:24 -0500
Michael Roth <mdroth@linux.vnet.ibm.com> wrote:

> From: Cornelia Huck <cohuck@redhat.com>
> 
> If a virtio device does not have legacy support, make sure that
> it is actually off, and bail out if not.
> 
> For virtio-pci, this means that any device without legacy support
> that has been specified to modern-only (or that has been forced
> to it) will work.
> 
> For virtio-ccw, this duplicates the check that is currently done
> prior to realization for any device that explicitly specified no
> support for legacy.
> 
> This catches devices that have not been fenced properly.
> 
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> Message-Id: <20200707105446.677966-3-cohuck@redhat.com>
> Cc: qemu-stable@nongnu.org
> Acked-by: Halil Pasic <pasic@linux.ibm.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> (cherry picked from commit 9b3a35ec8236933ab958a4c3ad883163f1ca66e7)
> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> ---
>  hw/s390x/virtio-ccw.c  | 6 ++++++
>  hw/virtio/virtio-pci.c | 4 ++++
>  2 files changed, 10 insertions(+)

I don't think we want to backport this (and the previous patch) to
stable. (Actually, my original patch didn't have the stable tag.)

This has flushed out several devices (mem, vsock, iommu) that should be
modern only, but weren't; unfortunately, this also breaks existing
command line invocations. We *might* consider including this together
with patches that force those devices to modern only, but I see only
the patch for virtio-mem has reached master yet.