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* kvm-unit-tests: Question about the "no interrupt when timer is disabled" case
@ 2020-07-23  8:56 Zenghui Yu
  2020-07-24 11:08 ` Alexandru Elisei
  0 siblings, 1 reply; 4+ messages in thread
From: Zenghui Yu @ 2020-07-23  8:56 UTC (permalink / raw)
  To: Alexandru Elisei; +Cc: Marc Zyngier, kvmarm

Hi Alexandru,

I've noticed that the timer case will fail in the -stable 4.19 kernel.
The log is as follows:

FAIL: vtimer-busy-loop: no interrupt when timer is disabled
FAIL: vtimer-busy-loop: interrupt signal no longer pending

And it's because the related fix [16e604a437c8, "KVM: arm/arm64: vgic:
Reevaluate level sensitive interrupts on enable"] hasn't been backported
to the stable tree.

Just out of curiosity, _without_ this fix, had you actually seen the
guest getting into trouble due to an un-retired level-sensitive
interrupt and your patch fixed it? Or this was found by code inspection?

Take the exact vtimer case as an example, is it possible that the Linux
guest would disable the vtimer (the input interrupt line is driven to 0
but the old KVM doesn't take this into account) and potentially hit this
issue? I'm not familiar with it.

One of our internal tree is based on the stable 4.19 and I'm sure this
fix is not included. But I havn't received any bad reports from our
users yet. But if there's any potential problem without this fix, it'd
good to get it properly backported. I can help to send a backport
request if so.


Thanks,
Zenghui
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2020-07-23  8:56 kvm-unit-tests: Question about the "no interrupt when timer is disabled" case Zenghui Yu
2020-07-24 11:08 ` Alexandru Elisei
2020-07-25  4:50   ` Zenghui Yu
2020-07-27 11:27     ` Alexandru Elisei

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