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Tsirkin" To: Jason Wang Cc: Halil Pasic , Cornelia Huck , linux-kernel , stable@vger.kernel.org, virtualization Subject: Re: [PATCH v2 2/2] virtio: acknowledge all features before access Message-ID: <20220119041343-mutt-send-email-mst@kernel.org> References: <20220118170225.30620-1-mst@redhat.com> <20220118170225.30620-2-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Jan 19, 2022 at 10:52:34AM +0800, Jason Wang wrote: > On Wed, Jan 19, 2022 at 1:04 AM Michael S. Tsirkin 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. > > So I guess this is for this part of the spec 3.1.1: > > """ > 4. Read device feature bits, and write the subset of feature bits > understood by the OS and driver to the device. During this step the > driver MAY read (but MUST NOT write) the device-specific configuration > fields to check that it can support the device before accepting it. > """ > > If it is, is this better to quote in the change log? I don't think this spec actually clarifies anything. Sent some spec patches to improve the situation. > Other than this, > > Acked-by: Jason Wang > > > > > 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" > > Signed-off-by: Michael S. Tsirkin > > > > fixup! virtio: acknowledge all features before access > > --- > > drivers/virtio/virtio.c | 39 ++++++++++++++++++++--------------- > > include/linux/virtio_config.h | 3 ++- > > 2 files changed, 24 insertions(+), 18 deletions(-) > > > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > > index d891b0a354b0..d6396be0ea83 100644 > > --- a/drivers/virtio/virtio.c > > +++ b/drivers/virtio/virtio.c > > @@ -166,14 +166,13 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status) > > } > > EXPORT_SYMBOL_GPL(virtio_add_status); > > > > -static int virtio_finalize_features(struct virtio_device *dev) > > +/* Do some validation, then set FEATURES_OK */ > > +static int virtio_features_ok(struct virtio_device *dev) > > { > > - int ret = dev->config->finalize_features(dev); > > unsigned status; > > + int ret; > > > > might_sleep(); > > - if (ret) > > - return ret; > > > > ret = arch_has_restricted_virtio_memory_access(); > > if (ret) { > > @@ -244,17 +243,6 @@ static int virtio_dev_probe(struct device *_d) > > driver_features_legacy = driver_features; > > } > > > > - /* > > - * Some devices detect legacy solely via F_VERSION_1. Write > > - * F_VERSION_1 to force LE config space accesses before FEATURES_OK for > > - * these when needed. > > - */ > > - if (drv->validate && !virtio_legacy_is_little_endian() > > - && device_features & BIT_ULL(VIRTIO_F_VERSION_1)) { > > - dev->features = BIT_ULL(VIRTIO_F_VERSION_1); > > - dev->config->finalize_features(dev); > > - } > > - > > if (device_features & (1ULL << VIRTIO_F_VERSION_1)) > > dev->features = driver_features & device_features; > > else > > @@ -265,13 +253,26 @@ static int virtio_dev_probe(struct device *_d) > > if (device_features & (1ULL << i)) > > __virtio_set_bit(dev, i); > > > > + err = dev->config->finalize_features(dev); > > + if (err) > > + goto err; > > + > > if (drv->validate) { > > + u64 features = dev->features; > > + > > err = drv->validate(dev); > > if (err) > > goto err; > > + > > + /* Did validation change any features? Then write them again. */ > > + if (features != dev->features) { > > + err = dev->config->finalize_features(dev); > > + if (err) > > + goto err; > > + } > > } > > > > - err = virtio_finalize_features(dev); > > + err = virtio_features_ok(dev); > > if (err) > > goto err; > > > > @@ -495,7 +496,11 @@ int virtio_device_restore(struct virtio_device *dev) > > /* We have a driver! */ > > virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER); > > > > - ret = virtio_finalize_features(dev); > > + ret = dev->config->finalize_features(dev); > > + if (ret) > > + goto err; > > + > > + ret = virtio_features_ok(dev); > > if (ret) > > goto err; > > > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > > index 4d107ad31149..dafdc7f48c01 100644 > > --- a/include/linux/virtio_config.h > > +++ b/include/linux/virtio_config.h > > @@ -64,8 +64,9 @@ struct virtio_shm_region { > > * 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 > > -- > > MST > > > > _______________________________________________ > Virtualization mailing list > Virtualization@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/virtualization >