Messages in this thread | | | From | Cornelia Huck <> | Subject | Re: [PATCH v2 2/2] virtio: acknowledge all features before access | Date | Thu, 20 Jan 2022 15:35:01 +0100 |
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On Tue, Jan 18 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 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). > > 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> > > fixup! virtio: acknowledge all features before access
Leftover from rebasing?
> --- > drivers/virtio/virtio.c | 39 ++++++++++++++++++++--------------- > include/linux/virtio_config.h | 3 ++- > 2 files changed, 24 insertions(+), 18 deletions(-)
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Would like to see a quick sanity test from Halil, though.
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