[PATCH V2 07/12] virtio-pci: harden INTX interrupts

Jason Wang
2021-10-12T06:53:43Z

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.

Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/virtio/virtio_pci_common.c | 24 ++++++++++++++++++++++--
drivers/virtio/virtio_pci_common.h | 1 +
2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 0b9523e6dd39..5ae6a2a4eb77 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -30,8 +30,16 @@ 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) {
+ /*
+ * 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(vp_dev->intx_soft_enabled, false);
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 +51,16 @@ 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) {
+ disable_irq(vp_dev->pci_dev->irq);
+ /*
+ * The above disable_irq() provides TSO ordering and
+ * as such promotes the below store to store-release.
+ */
+ WRITE_ONCE(vp_dev->intx_soft_enabled, true);
+ enable_irq(vp_dev->pci_dev->irq);
return;
+ }

for (i = 0; i < vp_dev->msix_vectors; ++i)
enable_irq(pci_irq_vector(vp_dev->pci_dev, i));
@@ -97,6 +113,10 @@ static irqreturn_t vp_interrupt(int irq, void *opaque)
struct virtio_pci_device *vp_dev = opaque;
u8 isr;

+ /* read intx_soft_enabled before read others */
+ if (!smp_load_acquire(&vp_dev->intx_soft_enabled))
+ return IRQ_NONE;
+
/* 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