Stefano pointed out the following situation:
----------------------
1) vcpuA/cpuA is running, it has already handled the event, cleared
evtchn_upcall_pending and EOIed the event_irq but hasn't trapped into
Xen yet. It is still in guest mode.
2) Xen on cpuB calls vcpu_mark_events_pending(vcpuA), then calls
vgic_inject_irq. However, because irq->line_level is high, it is not
injected.
3) vcpuA has to wait until trapping into Xen, calling
vcpu_update_evtchn_irq, and going back to guest mode before receiving
the event. This is theoretically a very long time.
----------------------
Fix this by updating the state of our emulated IRQ line level inside
vcpu_mark_events_pending(), before trying to inject the new interrupt.
Despite having two calls to vgic_inject_irq(), only one will actually do
something:
- If the emulated line level was already in sync with the actual flag,
the VGIC ignores the first call, due to vgic_validate_injection().
- If the emulated line level was high, but the flag says it should have
been low, vgic_inject_irq() will just update the line_level state.
- If the emulated line level was low, but the flags says it should have
been high, we will inject the interrupt. The second call is then a
NOP.
Signed-off-by: Andre Przywara <andre.przyw...@linaro.org>
---
Hi,
this would ideally have been part of a former patch:
"[PATCH v3 06/39] ARM: evtchn: Handle level triggered IRQs correctly",
but this has been merged already, so this has to be a follow-up.
Ideally this would be merged before the final patch that introduces the
CONFIG_NEW_VGIC Kconfig symbol, so that the old code gets never compiled.
Thanks,
Andre
xen/arch/arm/domain.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 9688e62f78..11fa9002dc 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -947,10 +947,17 @@ void vcpu_mark_events_pending(struct vcpu *v)
int already_pending = test_and_set_bit(
0, (unsigned long *)&vcpu_info(v, evtchn_upcall_pending));
- if ( already_pending )
- return;
+#ifdef CONFIG_NEW_VGIC
+ /* Update the state of the current interrupt line. */
+ vgic_inject_irq(v->domain, v, v->domain->arch.evtchn_irq, already_pending);
+ /* Make the level IRQ pending. That's a NOP if it was already. */
vgic_inject_irq(v->domain, v, v->domain->arch.evtchn_irq, true);
+#else
+ /* Only signal the VGIC if it wasn't already pending. */
+ if ( !already_pending )
+ vgic_inject_irq(v->domain, v, v->domain->arch.evtchn_irq, true);
+#endif
}
void vcpu_update_evtchn_irq(struct vcpu *v)
--
2.14.1
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