[Qemu-devel] [PATCH v2] e1000e: Prevent MSI/MSI-X storms

[Jan Kiszka]

From: Jan Kiszka <jan.kis...@siemens.com>

Only signal MSI/MSI-X events on rising edges. So far we re-triggered the
interrupt sources even if the guest did no consumed the pending one,
easily causing interrupt storms.

Issue was observable with Linux 4.16 e1000e driver when MSI-X was used.
Vector 2 was causing interrupt storms after the driver activated the
device.

Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
---

Changes in v2:
 - also update msi_causes_pending after EIAC changes (required because
   there is no e1000e_update_interrupt_state after that

 hw/net/e1000e_core.c | 11 +++++++++++
 hw/net/e1000e_core.h |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c
index c93c4661ed..d6ddd59986 100644
--- a/hw/net/e1000e_core.c
+++ b/hw/net/e1000e_core.c
@@ -2027,6 +2027,7 @@ e1000e_msix_notify_one(E1000ECore *core, uint32_t cause, 
uint32_t int_cfg)
     }
 
     core->mac[ICR] &= ~effective_eiac;
+    core->msi_causes_pending &= ~effective_eiac;
 
     if (!(core->mac[CTRL_EXT] & E1000_CTRL_EXT_IAME)) {
         core->mac[IMS] &= ~effective_eiac;
@@ -2123,6 +2124,13 @@ e1000e_send_msi(E1000ECore *core, bool msix)
 {
     uint32_t causes = core->mac[ICR] & core->mac[IMS] & ~E1000_ICR_ASSERTED;
 
+    core->msi_causes_pending &= causes;
+    causes ^= core->msi_causes_pending;
+    if (causes == 0) {
+        return;
+    }
+    core->msi_causes_pending |= causes;
+
     if (msix) {
         e1000e_msix_notify(core, causes);
     } else {
@@ -2160,6 +2168,9 @@ e1000e_update_interrupt_state(E1000ECore *core)
     core->mac[ICS] = core->mac[ICR];
 
     interrupts_pending = (core->mac[IMS] & core->mac[ICR]) ? true : false;
+    if (!interrupts_pending) {
+        core->msi_causes_pending = 0;
+    }
 
     trace_e1000e_irq_pending_interrupts(core->mac[ICR] & core->mac[IMS],
                                         core->mac[ICR], core->mac[IMS]);
diff --git a/hw/net/e1000e_core.h b/hw/net/e1000e_core.h
index 7d8ff41890..63a15510cc 100644
--- a/hw/net/e1000e_core.h
+++ b/hw/net/e1000e_core.h
@@ -109,6 +109,8 @@ struct E1000Core {
     NICState *owner_nic;
     PCIDevice *owner;
     void (*owner_start_recv)(PCIDevice *d);
+
+    uint32_t msi_causes_pending;
 };
 
 void
-- 
2.13.6