On Thu, Dec 9, 2021 at 4:27 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Fri, Nov 26, 2021 at 12:41:02PM +0800, Jason Wang wrote:
> > This patch tries to make sure the virtio interrupt handler for MMIO
> > won't be called after a reset and before virtio_device_ready(). We
> > can't use IRQF_NO_AUTOEN since we're using shared interrupt
> > (IRQF_SHARED). So this patch tracks the interrupt enabling status in a
> > new intr_soft_enabled variable and toggle it during in
> > vm_disable/enable_interrupts(). The MMIO interrupt handler will check
> > intr_soft_enabled before processing the actual interrupt.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> > Changes since V1:
> > - Silent compling warnings
> > drivers/virtio/virtio_mmio.c | 37 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 37 insertions(+)
> >
> > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> > index 56128b9c46eb..c517afdd2cc5 100644
> > --- a/drivers/virtio/virtio_mmio.c
> > +++ b/drivers/virtio/virtio_mmio.c
> > @@ -90,6 +90,7 @@ struct virtio_mmio_device {
> > /* a list of queues so we can dispatch IRQs */
> > spinlock_t lock;
> > struct list_head virtqueues;
> > + bool intr_soft_enabled;
> > };
> >
> > struct virtio_mmio_vq_info {
> > @@ -100,7 +101,37 @@ struct virtio_mmio_vq_info {
> > struct list_head node;
> > };
> >
> > +/* disable irq handlers */
> > +static void vm_disable_cbs(struct virtio_device *vdev)
> > +{
> > + struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> > + int irq = platform_get_irq(vm_dev->pdev, 0);
> >
> > + /*
> > + * The below synchronize() guarantees that any
> > + * interrupt for this line arriving after
> > + * synchronize_irq() has completed is guaranteed to see
> > + * intx_soft_enabled == false.
> > + */
> > + WRITE_ONCE(vm_dev->intr_soft_enabled, false);
> > + synchronize_irq(irq);
> > +}
> > +
> > +/* enable irq handlers */
> > +static void vm_enable_cbs(struct virtio_device *vdev)
> > +{
> > + struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> > + int irq = platform_get_irq(vm_dev->pdev, 0);
> > +
> > + disable_irq(irq);
> > + /*
> > + * The above disable_irq() provides TSO ordering and
> > + * as such promotes the below store to store-release.
> > + */
> > + WRITE_ONCE(vm_dev->intr_soft_enabled, true);
> > + enable_irq(irq);
> > + return;
> > +}
> >
> > /* Configuration interface */
> >
> > @@ -262,6 +293,8 @@ static void vm_reset(struct virtio_device *vdev)
> >
> > /* 0 status means a reset. */
> > writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
>
> There was a discussion about reading status to make sure it is clear.
> The spec says we should, this can't hurt as a further hardening measure.
> In fact, let's do it in the core maybe? Spec says it applies to all
> devices ...
We can do that, but I'm not sure if we break some existing device.
>
> > + /* Disable VQ/configuration callbacks. */
> > + vm_disable_cbs(vdev);
> > }
> >
> >
> > @@ -288,6 +321,9 @@ static irqreturn_t vm_interrupt(int irq, void *opaque)
> > unsigned long flags;
> > irqreturn_t ret = IRQ_NONE;
> >
> > + if (!READ_ONCE(vm_dev->intr_soft_enabled))
> > + return IRQ_NONE;
> > +
>
> So if the write is seen before reset happened (should not happen, but we
> are talking a buggy device) then it won't be acknowledged and device
> will keep pulling the interrupt. I think as long as we are hardening
> this, let's go the full mile and try to avoid DoS if we can, do the
> check before invoking the callback, but do not skip the read.
> Whether to still return IRQ_NONE is a good question.
Did you mean something like this:
/* Read and acknowledge interrupts */
status = readl(vm_dev->base + VIRTIO_MMIO_INTERRUPT_STATUS);
writel(status, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
if (status)
ret = IRQ_HANDLED;
if (!READ_ONCE(vm_dev->intr_soft_enabled))
return ret;
Thanks
>
>
>
>
> > /* Read and acknowledge interrupts */
> > status = readl(vm_dev->base + VIRTIO_MMIO_INTERRUPT_STATUS);
> > writel(status, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
> > @@ -529,6 +565,7 @@ static bool vm_get_shm_region(struct virtio_device *vdev,
> > }
> >
> > static const struct virtio_config_ops virtio_mmio_config_ops = {
> > + .enable_cbs = vm_enable_cbs,
> > .get = vm_get,
> > .set = vm_set,
> > .generation = vm_generation,
> > --
> > 2.25.1
>
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