Re: [PATCH V6 8/9] virtio: harden vring IRQ

Michael S. Tsirkin
2022-06-11T05:12:50Z

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@linutronix.de>
> 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 ?

> ---
> 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