On Tue, Jun 14, 2022 at 11:49 PM Michael S. Tsirkin <mst at redhat.com>
wrote:>
> On Tue, Jun 14, 2022 at 03:40:21PM +0800, Jason Wang wrote:
> > On Mon, Jun 13, 2022 at 5:28 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
> > >
> > > On Mon, Jun 13, 2022 at 05:14:59PM +0800, Jason Wang wrote:
> > > > On Mon, Jun 13, 2022 at 5:08 PM Jason Wang <jasowang at
redhat.com> wrote:
> > > > >
> > > > > On Mon, Jun 13, 2022 at 4:59 PM Michael S. Tsirkin
<mst at redhat.com> wrote:
> > > > > >
> > > > > > On Mon, Jun 13, 2022 at 04:51:08PM +0800, Jason
Wang wrote:
> > > > > > > On Mon, Jun 13, 2022 at 4:19 PM Michael S.
Tsirkin <mst at redhat.com> wrote:
> > > > > > > >
> > > > > > > > On Mon, Jun 13, 2022 at 04:07:09PM
+0800, Jason Wang wrote:
> > > > > > > > > On Mon, Jun 13, 2022 at 3:23 PM
Michael S. Tsirkin <mst at redhat.com> wrote:
> > > > > > > > > >
> > > > > > > > > > On Mon, Jun 13, 2022 at
01:26:59PM +0800, Jason Wang wrote:
> > > > > > > > > > > On Sat, Jun 11, 2022 at
1:12 PM Michael S. Tsirkin <mst at redhat.com> wrote:
> > > > > > > > > > > >
> > > > > > > > > > > > On Fri, May 27, 2022
at 02:01:19PM +0800, Jason Wang wrote:
> > > > > > > > > > > > > This is a
rework on the previous IRQ hardening that is done for
> > > > > > > > > > > > > virtio-pci
where several drawbacks were found and were reverted:
> > > > > > > > > > > > >
> > > > > > > > > > > > > 1) try to use
IRQF_NO_AUTOEN which is not friendly to affinity managed IRQ
> > > > > > > > > > > > > that is used
by some device such as virtio-blk
> > > > > > > > > > > > > 2) done only
for PCI transport
> > > > > > > > > > > > >
> > > > > > > > > > > > > The
vq->broken is re-used in this patch for implementing the IRQ
> > > > > > > > > > > > > hardening. The
vq->broken is set to true during both initialization
> > > > > > > > > > > > > and reset. And
the vq->broken is set to false in
> > > > > > > > > > > > >
virtio_device_ready(). Then vring_interrupt() can check and return
> > > > > > > > > > > > > when
vq->broken is true. And in this case, switch to return IRQ_NONE
> > > > > > > > > > > > > to let the
interrupt core aware of such invalid interrupt to prevent
> > > > > > > > > > > > > IRQ storm.
> > > > > > > > > > > > >
> > > > > > > > > > > > > The reason of
using a per queue variable instead of a per device one
> > > > > > > > > > > > > is that we may
need it for per queue reset hardening in the future.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Note that the
hardening is only done for vring interrupt since the
> > > > > > > > > > > > > config
interrupt hardening is already done in commit 22b7050a024d7
> > > > > > > > > > > > > ("virtio:
defer config changed notifications"). But the method that is
> > > > > > > > > > > > > used by config
interrupt can't be reused by the vring interrupt
> > > > > > > > > > > > > handler because
it uses spinlock to do the synchronization which is
> > > > > > > > > > > > > expensive.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Cc: Thomas
Gleixner <tglx at linutronix.de>
> > > > > > > > > > > > > Cc: Peter
Zijlstra <peterz at infradead.org>
> > > > > > > > > > > > > Cc: "Paul
E. McKenney" <paulmck at kernel.org>
> > > > > > > > > > > > > Cc: Marc
Zyngier <maz at kernel.org>
> > > > > > > > > > > > > Cc: Halil Pasic
<pasic at linux.ibm.com>
> > > > > > > > > > > > > Cc: Cornelia
Huck <cohuck at redhat.com>
> > > > > > > > > > > > > Cc: Vineeth
Vijayan <vneethv at linux.ibm.com>
> > > > > > > > > > > > > Cc: Peter
Oberparleiter <oberpar at linux.ibm.com>
> > > > > > > > > > > > > Cc: linux-s390
at vger.kernel.org
> > > > > > > > > > > > > Signed-off-by:
Jason Wang <jasowang at redhat.com>
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > Jason, I am really
concerned by all the fallout.
> > > > > > > > > > > > I propose adding a
flag to suppress the hardening -
> > > > > > > > > > > > this will be a
debugging aid and a work around for
> > > > > > > > > > > > users if we find
more buggy drivers.
> > > > > > > > > > > >
> > > > > > > > > > > >
suppress_interrupt_hardening ?
> > > > > > > > > > >
> > > > > > > > > > > I can post a patch but
I'm afraid if we disable it by default, it
> > > > > > > > > > > won't be used by the
users so there's no way for us to receive the bug
> > > > > > > > > > > report. Or we need a plan
to enable it by default.
> > > > > > > > > > >
> > > > > > > > > > > It's rc2, how about
waiting for 1 and 2 rc? Or it looks better if we
> > > > > > > > > > > simply warn instead of
disable it by default.
> > > > > > > > > > >
> > > > > > > > > > > Thanks
> > > > > > > > > >
> > > > > > > > > > I meant more like a flag in
struct virtio_driver.
> > > > > > > > > > For now, could you audit all
drivers which don't call _ready?
> > > > > > > > > > I found 5 of these:
> > > > > > > > > >
> > > > > > > > > > drivers/bluetooth/virtio_bt.c
> > > > > > > > >
> > > > > > > > > This driver seems to be fine, it
doesn't use the device/vq in its probe().
> > > > > > > >
> > > > > > > >
> > > > > > > > But it calls hci_register_dev and that
in turn queues all kind of
> > > > > > > > work. Also, can linux start using the
device immediately after
> > > > > > > > it's registered?
> > > > > > >
> > > > > > > So I think the driver is allowed to queue
before DRIVER_OK.
> > > > > >
> > > > > > it's not allowed to kick
> > > > >
> > > > > Yes.
> > > > >
> > > > > >
> > > > > > > If yes,
> > > > > > > the only side effect is the delay of the tx
interrupt after DRIVER_OK
> > > > > > > for a well behaved device.
> > > > > >
> > > > > > your patches drop the interrupt though, it
won't be just delayed.
> > > > >
> > > > > For a well behaved device, it can only trigger the
interrupt after DRIVER_OK.
> > > > >
> > > > > So for virtio bt, it works like:
> > > > >
> > > > > 1) driver queue buffer and kick
> > > > > 2) driver set DRIVER_OK
> > > > > 3) device start to process the buffer
> > > > > 4) device send an notification
> > > > >
> > > > > The only risk is that the virtqueue could be filled
before DRIVER_OK,
> > > > > or anything I missed?
> > > >
> > > > btw, hci has an open and close method and we do rx refill in
> > > > hdev->open, so we're probably fine here.
> > > >
> > > > Thanks
> > >
> > >
> > > Sounds good. Now to audit the rest of them from this POV ;)
> >
> > Adding maintainers.
> >
> > >
> > > drivers/i2c/busses/i2c-virtio.c
> >
> > It looks to me the device could be used immediately after
> > i2c_add_adapter() return. So we probably need to add
> > virtio_device_ready() before that. Fortunately, there's no rx vq
in
> > i2c and the callback looks safe if the callback is called before the
> > i2c registration and after virtio_device_ready().
> >
> > > drivers/net/caif/caif_virtio.c
> >
> > A networking device, RX is backed by vringh so we don't need to
> > refill. TX is backed by virtio and is available until ndo_open. So
> > it's fine to let the core to set DRIVER_OK after probe().
> >
> > > drivers/nvdimm/virtio_pmem.c
> >
> > It doesn't use interrupt so far, so it has nothing to do with the
IRQ hardening.
> >
> > But the device could be used by the subsystem immediately after
> > nvdimm_pmem_region_create(), this means the flush could be issued
> > before DRIVER_OK. We need virtio_device_ready() before. We don't
have
> > a RX virtqueue and the callback looks safe if the callback is called
> > after virtio_device_ready() but before the nvdimm region creating.
> >
> > And it looks to me there's a race between the assignment of
> > provider_data and virtio_pmem_flush(). If the flush was issued before
> > the assignment we will end up with a NULL pointer dereference. This is
> > something we need to fix.
> >
> > > arm_scmi
> >
> > It looks to me the singleton device could be used by SCMI immediately
after
> >
> > /* Ensure initialized scmi_vdev is visible */
> > smp_store_mb(scmi_vdev, vdev);
> >
> > So we probably need to do virtio_device_ready() before that. It has an
> > optional rx queue but the filling is done after the above assignment,
> > so it's safe. And the callback looks safe is a callback is
triggered
> > after virtio_device_ready() buy before the above assignment.
> >
> > > virtio_rpmsg_bus.c
> > >
> >
> > This is somehow more complicated. It has an rx queue, the rx filling
> > is done before virtio_device_ready() but the kick is done after. And
> > it looks to me the device could be used by subsystem immediately
> > rpmsg_virtio_add_ctrl_dev() returns.
> >
> > This means, if we do virtio_device_ready() after
> > rpmsg_virtio_add_ctrl_dev(), we may get kick before DRIVER_OK. If we
> > do virtio_device_ready() before rpmsg_virtio_add_ctrl_dev(),
there's a
> > race between the callbacks and rpmsg_virtio_add_ctrl_dev() that could
> > be exploited.
> >
> > It requires more thoughts.
> >
> > Thanks
>
> I think at this point let's do it before so we at least do not
> get a regression with your patches, add a big comment and work
> on fixing properly in the next Linux version. Do you think you can
> commit to a full fix in the next linux version?
I think it should be ok.
If I understand you correctly, you meant to disable the hardening in
this release?
(Actually, my understanding is that since we are developing mainline
instead of a downstream version with a hardening features, bug reports
are somehow expected, especially consider most of the bugs are not
related to hardening itself)
Thanks
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 13a7348cedff..7ef3115efbad 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1688,7 +1688,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
vq->we_own_ring = true;
vq->notify = notify;
vq->weak_barriers = weak_barriers;
- vq->broken = true;
+ vq->broken = false;
vq->last_used_idx = 0;
vq->event_triggered = false;
vq->num_added = 0;
>
>
> > >
> > >
> > > > >
> > > > > >
> > > > > > > If not, we need to clarify it in the spec
> > > > > > > and call virtio_device_ready() before
subsystem registration.
> > > > > >
> > > > > > hmm, i don't get what we need to clarify
> > > > >
> > > > > E.g the driver is not allowed to kick or after
DRIVER_OK should the
> > > > > device only process the buffer after a kick after
DRIVER_OK (I think
> > > > > no)?
> > > > >
> > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > > >
drivers/gpu/drm/virtio/virtgpu_drv.c
> > > > > > > > >
> > > > > > > > > It calles virtio_device_ready() in
virtio_gpu_init(), and it looks to
> > > > > > > > > me the code is correct.
> > > > > > > >
> > > > > > > > OK.
> > > > > > > >
> > > > > > > > > >
drivers/i2c/busses/i2c-virtio.c
> > > > > > > > > > drivers/net/caif/caif_virtio.c
> > > > > > > > > > drivers/nvdimm/virtio_pmem.c
> > > > > > > > >
> > > > > > > > > The above looks fine and we have
three more:
> > > > > > > > >
> > > > > > > > > arm_scmi: probe() doesn't use
vq
> > > > > > > > > mac80211_hwsim.c: doesn't use
vq (only fill rx), but it kicks the rx,
> > > > > > > > > it looks to me we need a
device_ready before the kick.
> > > > > > > > > virtio_rpmsg_bus.c: doesn't use
vq
> > > > > > > > >
> > > > > > > > > I will post a patch for
mac80211_hwsim.c.
> > > > > > > > > Thanks
> > > > > > > >
> > > > > > > > Same comments for all of the above.
Might linux not start using the
> > > > > > > > device once it's registered?
> > > > > > >
> > > > > > > It depends on the specific subsystem.
> > > > > > >
> > > > > > > For the subsystem that can't use the
device immediately, calling
> > > > > > > virtio_device_ready() after the
subsystem's registration should be
> > > > > > > fine. E.g for the networking subsystem, the
TX won't happen if
> > > > > > > ndo_open() is not called, calling
virtio_device_ready() after
> > > > > > > netdev_register() seems to be fine.
> > > > > >
> > > > > > exactly
> > > > > >
> > > > > > > For the subsystem that can use the device
immediately, if the
> > > > > > > subsystem does not depend on the result of a
request in the probe to
> > > > > > > proceed, we are still fine. Since those
requests will be proceed after
> > > > > > > DRIVER_OK.
> > > > > >
> > > > > > Well first won't driver code normally kick as
well?
> > > > >
> > > > > Kick itself is not blocked.
> > > > >
> > > > > > And without kick, won't everything just be
blocked?
> > > > >
> > > > > It depends on the subsystem. E.g driver can choose to
use a callback
> > > > > instead of polling the used buffer in the probe.
> > > > >
> > > > > >
> > > > > >
> > > > > > > For the rest we need to do
virtio_device_ready() before registration.
> > > > > > >
> > > > > > > Thanks
> > > > > >
> > > > > > Then we can get an interrupt for an unregistered
device.
> > > > >
> > > > > It depends on the device. For the device that
doesn't have an rx queue
> > > > > (or device to driver queue), we are fine:
> > > > >
> > > > > E.g in virtio-blk:
> > > > >
> > > > > virtio_device_ready(vdev);
> > > > >
> > > > > err = device_add_disk(&vdev->dev,
vblk->disk, virtblk_attr_groups);
> > > > > if (err)
> > > > > goto out_cleanup_disk;
> > > > >
> > > > > Thanks
> > > > >
> > > > > >
> > > > > >
> > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > > ---
> > > > > > > > > > > > >
drivers/s390/virtio/virtio_ccw.c | 4 ++++
> > > > > > > > > > > > >
drivers/virtio/virtio.c | 15 ++++++++++++---
> > > > > > > > > > > > >
drivers/virtio/virtio_mmio.c | 5 +++++
> > > > > > > > > > > > >
drivers/virtio/virtio_pci_modern_dev.c | 5 +++++
> > > > > > > > > > > > >
drivers/virtio/virtio_ring.c | 11 +++++++----
> > > > > > > > > > > > >
include/linux/virtio_config.h | 20 ++++++++++++++++++++
> > > > > > > > > > > > > 6 files
changed, 53 insertions(+), 7 deletions(-)
> > > > > > > > > > > > >
> > > > > > > > > > > > > diff --git
a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > > > > > > > > > > > > index
c188e4f20ca3..97e51c34e6cf 100644
> > > > > > > > > > > > > ---
a/drivers/s390/virtio/virtio_ccw.c
> > > > > > > > > > > > > +++
b/drivers/s390/virtio/virtio_ccw.c
> > > > > > > > > > > > > @@ -971,6
+971,10 @@ static void virtio_ccw_set_status(struct virtio_device *vdev, u8
status)
> > > > > > > > > > > > >
ccw->flags = 0;
> > > > > > > > > > > > >
ccw->count = sizeof(status);
> > > > > > > > > > > > >
ccw->cda = (__u32)(unsigned long)&vcdev->dma_area->status;
> > > > > > > > > > > > > + /* We use
ssch for setting the status which is a serializing
> > > > > > > > > > > > > + *
instruction that guarantees the memory writes have
> > > > > > > > > > > > > + *
completed before ssch.
> > > > > > > > > > > > > + */
> > > > > > > > > > > > > ret =
ccw_io_helper(vcdev, ccw, VIRTIO_CCW_DOING_WRITE_STATUS);
> > > > > > > > > > > > > /* Write
failed? We assume status is unchanged. */
> > > > > > > > > > > > > if (ret)
> > > > > > > > > > > > > diff --git
a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > > > > > > > > > > > > index
aa1eb5132767..95fac4c97c8b 100644
> > > > > > > > > > > > > ---
a/drivers/virtio/virtio.c
> > > > > > > > > > > > > +++
b/drivers/virtio/virtio.c
> > > > > > > > > > > > > @@ -220,6
+220,15 @@ static int virtio_features_ok(struct virtio_device *dev)
> > > > > > > > > > > > > * */
> > > > > > > > > > > > > void
virtio_reset_device(struct virtio_device *dev)
> > > > > > > > > > > > > {
> > > > > > > > > > > > > + /*
> > > > > > > > > > > > > + * The
below virtio_synchronize_cbs() guarantees that any
> > > > > > > > > > > > > + *
interrupt for this line arriving after
> > > > > > > > > > > > > + *
virtio_synchronize_vqs() has completed is guaranteed to see
> > > > > > > > > > > > > + *
vq->broken as true.
> > > > > > > > > > > > > + */
> > > > > > > > > > > > > +
virtio_break_device(dev);
> > > > > > > > > > > >
> > > > > > > > > > > > So make this
conditional
> > > > > > > > > > > >
> > > > > > > > > > > > > +
virtio_synchronize_cbs(dev);
> > > > > > > > > > > > > +
> > > > > > > > > > > > >
dev->config->reset(dev);
> > > > > > > > > > > > > }
> > > > > > > > > > > > >
EXPORT_SYMBOL_GPL(virtio_reset_device);
> > > > > > > > > > > > > @@ -428,6
+437,9 @@ int register_virtio_device(struct virtio_device *dev)
> > > > > > > > > > > > >
dev->config_enabled = false;
> > > > > > > > > > > > >
dev->config_change_pending = false;
> > > > > > > > > > > > >
> > > > > > > > > > > > > +
INIT_LIST_HEAD(&dev->vqs);
> > > > > > > > > > > > > +
spin_lock_init(&dev->vqs_list_lock);
> > > > > > > > > > > > > +
> > > > > > > > > > > > > /* We
always start by resetting the device, in case a previous
> > > > > > > > > > > > > * driver
messed it up. This also tests that code path a little. */
> > > > > > > > > > > > >
virtio_reset_device(dev);
> > > > > > > > > > > > > @@ -435,9
+447,6 @@ int register_virtio_device(struct virtio_device *dev)
> > > > > > > > > > > > > /*
Acknowledge that we've seen the device. */
> > > > > > > > > > > > >
virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
> > > > > > > > > > > > >
> > > > > > > > > > > > > -
INIT_LIST_HEAD(&dev->vqs);
> > > > > > > > > > > > > -
spin_lock_init(&dev->vqs_list_lock);
> > > > > > > > > > > > > -
> > > > > > > > > > > > > /*
> > > > > > > > > > > > > *
device_add() causes the bus infrastructure to look for a matching
> > > > > > > > > > > > > *
driver.
> > > > > > > > > > > > > diff --git
a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> > > > > > > > > > > > > index
c9699a59f93c..f9a36bc7ac27 100644
> > > > > > > > > > > > > ---
a/drivers/virtio/virtio_mmio.c
> > > > > > > > > > > > > +++
b/drivers/virtio/virtio_mmio.c
> > > > > > > > > > > > > @@ -253,6
+253,11 @@ static void vm_set_status(struct virtio_device *vdev, u8 status)
> > > > > > > > > > > > > /* We
should never be setting status to 0. */
> > > > > > > > > > > > >
BUG_ON(status == 0);
> > > > > > > > > > > > >
> > > > > > > > > > > > > + /*
> > > > > > > > > > > > > + * Per
memory-barriers.txt, wmb() is not needed to guarantee
> > > > > > > > > > > > > + * that
the the cache coherent memory writes have completed
> > > > > > > > > > > > > + * before
writing to the MMIO region.
> > > > > > > > > > > > > + */
> > > > > > > > > > > > >
writel(status, vm_dev->base + VIRTIO_MMIO_STATUS);
> > > > > > > > > > > > > }
> > > > > > > > > > > > >
> > > > > > > > > > > > > diff --git
a/drivers/virtio/virtio_pci_modern_dev.c
b/drivers/virtio/virtio_pci_modern_dev.c
> > > > > > > > > > > > > index
4093f9cca7a6..a0fa14f28a7f 100644
> > > > > > > > > > > > > ---
a/drivers/virtio/virtio_pci_modern_dev.c
> > > > > > > > > > > > > +++
b/drivers/virtio/virtio_pci_modern_dev.c
> > > > > > > > > > > > > @@ -467,6
+467,11 @@ void vp_modern_set_status(struct virtio_pci_modern_device *mdev,
> > > > > > > > > > > > > {
> > > > > > > > > > > > > struct
virtio_pci_common_cfg __iomem *cfg = mdev->common;
> > > > > > > > > > > > >
> > > > > > > > > > > > > + /*
> > > > > > > > > > > > > + * Per
memory-barriers.txt, wmb() is not needed to guarantee
> > > > > > > > > > > > > + * that
the the cache coherent memory writes have completed
> > > > > > > > > > > > > + * before
writing to the MMIO region.
> > > > > > > > > > > > > + */
> > > > > > > > > > > > >
vp_iowrite8(status, &cfg->device_status);
> > > > > > > > > > > > > }
> > > > > > > > > > > > >
EXPORT_SYMBOL_GPL(vp_modern_set_status);
> > > > > > > > > > > > > diff --git
a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > > > > > > > > > > index
9c231e1fded7..13a7348cedff 100644
> > > > > > > > > > > > > ---
a/drivers/virtio/virtio_ring.c
> > > > > > > > > > > > > +++
b/drivers/virtio/virtio_ring.c
> > > > > > > > > > > > > @@ -1688,7
+1688,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
> > > > > > > > > > > > >
vq->we_own_ring = true;
> > > > > > > > > > > > >
vq->notify = notify;
> > > > > > > > > > > > >
vq->weak_barriers = weak_barriers;
> > > > > > > > > > > > > -
vq->broken = false;
> > > > > > > > > > > > > +
vq->broken = true;
> > > > > > > > > > > > >
vq->last_used_idx = 0;
> > > > > > > > > > > > >
vq->event_triggered = false;
> > > > > > > > > > > > >
vq->num_added = 0;
> > > > > > > > > > > >
> > > > > > > > > > > > and make this
conditional
> > > > > > > > > > > >
> > > > > > > > > > > > > @@ -2134,8
+2134,11 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
> > > > > > > > > > > > >
return IRQ_NONE;
> > > > > > > > > > > > > }
> > > > > > > > > > > > >
> > > > > > > > > > > > > - if
(unlikely(vq->broken))
> > > > > > > > > > > > > -
return IRQ_HANDLED;
> > > > > > > > > > > > > + if
(unlikely(vq->broken)) {
> > > > > > > > > > > > > +
dev_warn_once(&vq->vq.vdev->dev,
> > > > > > > > > > > > > +
"virtio vring IRQ raised before DRIVER_OK");
> > > > > > > > > > > > > +
return IRQ_NONE;
> > > > > > > > > > > > > + }
> > > > > > > > > > > > >
> > > > > > > > > > > > > /* Just a
hint for performance: so it's ok that this can be racy! */
> > > > > > > > > > > > > if
(vq->event)
> > > > > > > > > > > > > @@ -2177,7
+2180,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> > > > > > > > > > > > >
vq->we_own_ring = false;
> > > > > > > > > > > > >
vq->notify = notify;
> > > > > > > > > > > > >
vq->weak_barriers = weak_barriers;
> > > > > > > > > > > > > -
vq->broken = false;
> > > > > > > > > > > > > +
vq->broken = true;
> > > > > > > > > > > > >
vq->last_used_idx = 0;
> > > > > > > > > > > > >
vq->event_triggered = false;
> > > > > > > > > > > > >
vq->num_added = 0;
> > > > > > > > > > > >
> > > > > > > > > > > > and make this
conditional
> > > > > > > > > > > >
> > > > > > > > > > > > > diff --git
a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > > > > > > > > > > > > index
25be018810a7..d4edfd7d91bb 100644
> > > > > > > > > > > > > ---
a/include/linux/virtio_config.h
> > > > > > > > > > > > > +++
b/include/linux/virtio_config.h
> > > > > > > > > > > > > @@ -256,6
+256,26 @@ void virtio_device_ready(struct virtio_device *dev)
> > > > > > > > > > > > > unsigned
status = dev->config->get_status(dev);
> > > > > > > > > > > > >
> > > > > > > > > > > > >
BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
> > > > > > > > > > > > > +
> > > > > > > > > > > > > + /*
> > > > > > > > > > > > > + * The
virtio_synchronize_cbs() makes sure vring_interrupt()
> > > > > > > > > > > > > + * will
see the driver specific setup if it sees vq->broken
> > > > > > > > > > > > > + * as
false (even if the notifications come before DRIVER_OK).
> > > > > > > > > > > > > + */
> > > > > > > > > > > > > +
virtio_synchronize_cbs(dev);
> > > > > > > > > > > > > +
__virtio_unbreak_device(dev);
> > > > > > > > > > > > > + /*
> > > > > > > > > > > > > + * The
transport should ensure the visibility of vq->broken
> > > > > > > > > > > > > + * before
setting DRIVER_OK. See the comments for the transport
> > > > > > > > > > > > > + *
specific set_status() method.
> > > > > > > > > > > > > + *
> > > > > > > > > > > > > + * A well
behaved device will only notify a virtqueue after
> > > > > > > > > > > > > + *
DRIVER_OK, this means the device should "see" the coherenct
> > > > > > > > > > > > > + * memory
write that set vq->broken as false which is done by
> > > > > > > > > > > > > + * the
driver when it sees DRIVER_OK, then the following
> > > > > > > > > > > > > + *
driver's vring_interrupt() will see vq->broken as false so
> > > > > > > > > > > > > + * we
won't lose any notification.
> > > > > > > > > > > > > + */
> > > > > > > > > > > > >
dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> > > > > > > > > > > > > }
> > > > > > > > > > > > >
> > > > > > > > > > > > > --
> > > > > > > > > > > > > 2.25.1
> > > > > > > > > > > >
> > > > > > > > > >
> > > > > > > >
> > > > > >
> > >
>