e1000e: Fix possible interrupt loss when using MSI

[PATCH] e1000e: Fix possible interrupt loss when using MSI

Posted by Ake Koomsin 1 year, 9 months ago

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>
---
 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 2c51089a82..208e3e0d79 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();
-- 
2.25.1

Re: [PATCH] e1000e: Fix possible interrupt loss when using MSI

Posted by Jason Wang 1 year, 9 months ago

On Wed, Jul 20, 2022 at 7:14 PM Ake Koomsin <ake@igel.co.jp> wrote:
>
> 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>

I've queued this.

Thanks

> ---
>  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 2c51089a82..208e3e0d79 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();
> --
> 2.25.1
>