diff options
author | Michael S. Tsirkin <mst@redhat.com> | 2022-01-14 14:58:41 -0500 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-03-16 13:21:48 +0100 |
commit | 635959a82154b6f86eabe142c578bf449854c9d3 (patch) | |
tree | 43537cfe36fcaf03c06336736d29e83932fb8895 /include | |
parent | ffeb42e05d7d8af2c03ed168b8d20da0d45cb622 (diff) |
virtio: acknowledge all features before access
commit 4fa59ede95195f267101a1b8916992cf3f245cdb upstream.
The feature negotiation was designed in a way that
makes it possible for devices to know which config
fields will be accessed by drivers.
This is broken since commit 404123c2db79 ("virtio: allow drivers to
validate features") with fallout in at least block and net. We have a
partial work-around in commit 2f9a174f918e ("virtio: write back
F_VERSION_1 before validate") which at least lets devices find out which
format should config space have, but this is a partial fix: guests
should not access config space without acknowledging features since
otherwise we'll never be able to change the config space format.
To fix, split finalize_features from virtio_finalize_features and
call finalize_features with all feature bits before validation,
and then - if validation changed any bits - once again after.
Since virtio_finalize_features no longer writes out features
rename it to virtio_features_ok - since that is what it does:
checks that features are ok with the device.
As a side effect, this also reduces the amount of hypervisor accesses -
we now only acknowledge features once unless we are clearing any
features when validating (which is uncommon).
IRC I think that this was more or less always the intent in the spec but
unfortunately the way the spec is worded does not say this explicitly, I
plan to address this at the spec level, too.
Acked-by: Jason Wang <jasowang@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 404123c2db79 ("virtio: allow drivers to validate features")
Fixes: 2f9a174f918e ("virtio: write back F_VERSION_1 before validate")
Cc: "Halil Pasic" <pasic@linux.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/virtio_config.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h index bb4cc4910750..ad4d4697a167 100644 --- a/include/linux/virtio_config.h +++ b/include/linux/virtio_config.h @@ -56,8 +56,9 @@ struct irq_affinity; * Returns the first 64 feature bits (all we currently need). * @finalize_features: confirm what device features we'll be using. * vdev: the virtio_device - * This gives the final feature bits for the device: it can change + * This sends the driver feature bits to the device: it can change * the dev->feature bits if it wants. + * Note: despite the name this can be called any number of times. * Returns 0 on success or error status * @bus_name: return the bus name associated with the device (optional) * vdev: the virtio_device |