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List:       kvm
Subject:    Re: ACPI timer test failure in kvm-unit-test
From:       Paolo Bonzini <pbonzini () redhat ! com>
Date:       2018-11-30 23:17:14
Message-ID: 25163e1a-0d46-6f99-e321-49a3137ceba1 () redhat ! com
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On 30/11/18 22:38, Wei Huang wrote:
> Obviously the
> code is expecting the APIC_TMCCT counter will be reset to the initial
> value stored in APIC_TMICT, right after the counter reach zero (it is a
> periodic timer anyway). However this assumption shouldn't be held true
> all the time. It is possible the test code will reads APIC_TMCCT before
> the reset happens. If this happens, the test will fail. In fact, in my
> experiment, it is quite common (>20% of chance) to see APIC_TMCCT 0 on
> Intel "E3-1220 V2" CPU.
> 

This is an emulated device, so I'm quite surprised that this can happen
only on one processor.  It is possible, or perhaps even likely, that you
stumbled upon a processor bug.

Can you try reloading kvm_intel with the enable_preemption_timer
parameter set to 0?  If it passes, we need to add that Xeon to the list
of broken CPUs, so that cpu_has_broken_vmx_preemption_timer filters it
out.  The only information needed for that is CPUID[1].EAX.

Thanks,

Paoo
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