Hi l4-hackers,
When running a virtual machine, I encounter an assertion failure after the VM
has been up for some time. The kernel crashes in
src/kern/arm/thread-arm-hyp.cpp, specifically in the function
vcpu_vgic_upcall(unsigned virq):
vcpu_vgic_upcall(unsigned virq)
{
......
assert(state() & Thread_vcpu_user);
......
}
Based on source code inspection and preliminary debugging, the problem seems to
be related to the management of the Thread_vcpu_user state.
（1）Under normal circumstances, the vcpu_resume path (transitioning from the
kernel back to the guest OS) updates the vCPU state to include
Thread_vcpu_user. However, if an interrupt is delivered during this transition
while the receiving side is not yet ready, the vCPU frequently return to the
kernel (via vcpu_return_to_kernel) and subsequently process the interrupt
through guest_irq in vcpu_entries. In this situation, the expected update of
Thread_vcpu_user may not yet have taken place, which seems result in the assert
being triggered when a VGIC interrupt is involved.
（2）A similar condition seems to occur in the vcpu_async_ipc path. At the end of
IPC handling, this function explicitly clears the Thread_vcpu_user flag. If a
VGIC interrupt is delivered during this phase, the absence of the expected
Thread_vcpu_user state seems to lead to the same assertion failure.
I would like to confirm if the two points above are correct, and what steps I
should take next to further debug this issue.
In addition, I have some assumptions I would like to confirm:
First, for IPC between non-vcpu threads, the L4 microkernel handles message
delivery and scheduling (wake/schedule) directly, without requiring any
forwarding through uvmm. Similarly, interrupts bound via the interrupt
controller (ICU) to a non-vcpu thread or handler are also managed by the kernel
and scheduler, and therefore do not necessarily involve uvmm.
Second, passthrough interrupts, when not delivered in direct-injection mode,
are routed to uvmm for handling if they are bound to a vCPU. Likewise, services
provided by uvmm (such as virq) are also bound to a vCPU and therefore require
forwarding through uvmm.
There seems to have been a similar question in the past, but it does not seem
to have been resolved.
Re: Assertion failure error in kernel vgic interrupt processing - l4-hackers -
OS Site
I wonder if my questions are related to that post, and if any solutions exist.
Thanks!
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