On Mon, Sep 13, 2021 at 2:33 PM Michael S. Tsirkin [off-list ref] wrote:

On Mon, Sep 13, 2021 at 01:53:51PM +0800, Jason Wang wrote:

quoted

This patch tries to make sure the virtio interrupt handler for INTX
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 INTX enabling status in a new
intx_soft_enabled variable and toggle it during in
vp_disable/enable_vectors(). The INTX interrupt handler will check
intx_soft_enabled before processing the actual interrupt.

Signed-off-by: Jason Wang <jasowang@redhat.com>

Not all that excited about all the memory barriers for something
that should be an extremely rare event (for most kernels -
literally once per boot). Can't we do better?

I'm not sure, but do we need to care about the slow path (INTX)?

(Or do you have a better approach?)

Thanks

quoted

---
 drivers/virtio/virtio_pci_common.c | 18 ++++++++++++++++--
 drivers/virtio/virtio_pci_common.h |  1 +
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 0b9523e6dd39..835197151dc1 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c

@@ -30,8 +30,12 @@ void vp_disable_vectors(struct virtio_device *vdev)
      struct virtio_pci_device *vp_dev = to_vp_device(vdev);
      int i;

-     if (vp_dev->intx_enabled)
+     if (vp_dev->intx_enabled) {
+             vp_dev->intx_soft_enabled = false;
+             /* ensure the vp_interrupt see this intx_soft_enabled value */
+             smp_wmb();
              synchronize_irq(vp_dev->pci_dev->irq);
+     }

      for (i = 0; i < vp_dev->msix_vectors; ++i)
              disable_irq(pci_irq_vector(vp_dev->pci_dev, i));

@@ -43,8 +47,12 @@ void vp_enable_vectors(struct virtio_device *vdev)
      struct virtio_pci_device *vp_dev = to_vp_device(vdev);
      int i;

-     if (vp_dev->intx_enabled)
+     if (vp_dev->intx_enabled) {
+             vp_dev->intx_soft_enabled = true;
+             /* ensure the vp_interrupt see this intx_soft_enabled value */
+             smp_wmb();
              return;
+     }

      for (i = 0; i < vp_dev->msix_vectors; ++i)
              enable_irq(pci_irq_vector(vp_dev->pci_dev, i));

@@ -97,6 +105,12 @@ static irqreturn_t vp_interrupt(int irq, void *opaque)
      struct virtio_pci_device *vp_dev = opaque;
      u8 isr;

+     if (!vp_dev->intx_soft_enabled)
+             return IRQ_NONE;
+
+     /* read intx_soft_enabled before read others */
+     smp_rmb();
+
      /* reading the ISR has the effect of also clearing it so it's very
       * important to save off the value. */
      isr = ioread8(vp_dev->isr);

diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
index a235ce9ff6a5..3c06e0f92ee4 100644
--- a/drivers/virtio/virtio_pci_common.h
+++ b/drivers/virtio/virtio_pci_common.h

@@ -64,6 +64,7 @@ struct virtio_pci_device {
      /* MSI-X support */
      int msix_enabled;
      int intx_enabled;
+     bool intx_soft_enabled;
      cpumask_var_t *msix_affinity_masks;
      /* Name strings for interrupts. This size should be enough,
       * and I'm too lazy to allocate each name separately. */
--

2.25.1

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