Message-ID: <20220613023337-mutt-send-email-mst@kernel.org>
Date:   Mon, 13 Jun 2022 03:23:39 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        eperezma <eperezma@...hat.com>, Cindy Lu <lulu@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH V6 8/9] virtio: harden vring IRQ

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@...hat.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@...utronix.de>
> > > Cc: Peter Zijlstra <peterz@...radead.org>
> > > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > > Cc: Marc Zyngier <maz@...nel.org>
> > > Cc: Halil Pasic <pasic@...ux.ibm.com>
> > > Cc: Cornelia Huck <cohuck@...hat.com>
> > > Cc: Vineeth Vijayan <vneethv@...ux.ibm.com>
> > > Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>
> > > Cc: linux-s390@...r.kernel.org
> > > Signed-off-by: Jason Wang <jasowang@...hat.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
drivers/gpu/drm/virtio/virtgpu_drv.c
drivers/i2c/busses/i2c-virtio.c
drivers/net/caif/caif_virtio.c
drivers/nvdimm/virtio_pmem.c




> >
> >
> > > ---
> > >  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
> >

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