Re: [Qemu-devel] [PATCH V3] rtc: fix a infinite loop in windowsvmstartup

[Paolo Bonzini]

On 26/07/2017 03:28, address@hidden wrote:
> 
> 
> when the problem happens , windows kernel is checking  whether REG_A_UIP is 
> changing after periodic timer has stopped. windows kernel access REG_A
> according to INB instrunction and it will spend several microseconds because
> of VM_EXIT. 

A vmexit to the RTC timer should be around 10.000 clock cycles, which is
less than a microsecond.

> update timer has changed to a long expire time (as alarm timer)on the
> one hand.
> 
> on the other hand  244 microseconds in one second is too short to hit
> the region.
> 
> windows kernel may check REG_A_UIP when considering RTC something wrong.
> many windows VM reboot at the same time and rtc periodic timer may delay
> badly..

Does Windows do this test when Hyper-V englightenments are enabled
(especially hv-relaxed)?

It seems to be a Windows issue to me.  I'm not sure adding hacks to the
device model is the right thing to do, especially because I don't
understand why your fix worked.

Paolo