On Mon, Jun 13, 2022 at 4:19 PM Michael S. Tsirkin [off-list ref] wrote:

On Mon, Jun 13, 2022 at 04:07:09PM +0800, Jason Wang wrote:

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On Mon, Jun 13, 2022 at 3:23 PM Michael S. Tsirkin [off-list ref] wrote:

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On Mon, Jun 13, 2022 at 01:26:59PM +0800, Jason Wang wrote:

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On Sat, Jun 11, 2022 at 1:12 PM Michael S. Tsirkin [off-list ref] wrote:

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On Fri, May 27, 2022 at 02:01:19PM +0800, Jason Wang wrote:

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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 <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Vineeth Vijayan <vneethv@linux.ibm.com>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Cc: linux-s390@vger.kernel.org
Signed-off-by: Jason Wang <jasowang@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. If yes,
the only side effect is the delay of the tx interrupt after DRIVER_OK
for a well behaved device. If not, we need to clarify it in the spec
and call virtio_device_ready() before subsystem registration.

quoted

quoted

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.

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quoted

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.

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.

For the rest we need to do virtio_device_ready() before registration.

Thanks

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---
 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

quoted

+     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

quoted

@@ -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

quoted

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

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