[PULL 1/3] e1000e: Fix possible interrupt loss when using MSI

[Jason Wang <jasowang@redhat.com>]

From: Ake Koomsin <ake@igel.co.jp>

Commit "e1000e: Prevent MSI/MSI-X storms" introduced msi_causes_pending
to prevent interrupt storms problem. It was tested with MSI-X.

In case of MSI, the guest can rely solely on interrupts to clear ICR.
Upon clearing all pending interrupts, msi_causes_pending gets cleared.
However, when e1000e_itr_should_postpone() in e1000e_send_msi() returns
true, MSI never gets fired by e1000e_intrmgr_on_throttling_timer()
because msi_causes_pending is still set. This results in interrupt loss.

To prevent this, we need to clear msi_causes_pending when MSI is going
to get fired by the throttling timer. The guest can then receive
interrupts eventually.

Signed-off-by: Ake Koomsin <ake@igel.co.jp>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/net/e1000e_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c
index 2c51089..208e3e0 100644
--- a/hw/net/e1000e_core.c
+++ b/hw/net/e1000e_core.c
@@ -159,6 +159,8 @@ e1000e_intrmgr_on_throttling_timer(void *opaque)
 
     if (msi_enabled(timer->core->owner)) {
         trace_e1000e_irq_msi_notify_postponed();
+        /* Clear msi_causes_pending to fire MSI eventually */
+        timer->core->msi_causes_pending = 0;
         e1000e_set_interrupt_cause(timer->core, 0);
     } else {
         trace_e1000e_irq_legacy_notify_postponed();
-- 
2.7.4