RE: [PATCH] vtdt: add a missing change (RE: [Xen-devel] Re: xen guest hang with TSC_DEADLINE)

["Wei, Gang" <gang.wei@xxxxxxxxx>]

Christoph Egger wrote on 2011-01-05:
>>>>>> c/s 22529 and 22530 cause a xen guest hang.
>>>>>> 
>>>>>> While "normal" guests like Linux and NetBSD boot fine I boot
>>>>>> Xen itself as a xen guest for my nested virtualization.
>>>>>> 
>>>>>> When I do that then the guest dom0 hangs at boot when it tries
>>>>>> to initialize the first vcpu.
>>>>>> The bug is introduced somewhere in c/s 22529 and triggers with
>>>>>> c/s 22530.
>>>>> 
>>>>> Can you enable apic_timer debug info var hvm_debug and give
>>>>> more serial port log around the guest dom0 hangs? I used to
>>>>> test xen guest, it works well expect that it boot a little bit slowly.
>>>> 
>>>> This is the log output I get with TSC_DEADLINE feature enabled:
>>> 
>>> Just found one change was missed while the whole patch was checked in.
>>> Apply below patch, it should be ok now.
>>> ...
>> 
>> The hang is still reproducable with this change. Sorry.
> 
> I took a deeper look into this problem.
> The guest dom0 depends on the xen clock to continue ticking.
> When the guest xen hypervisor uses the TSC Deadline Timer then the xen
> clock for the guest dom0 does not continue ticking.
> By "xen clock" I mean the timer a PV guest uses.
> 
> When the dom0 initializes the first virtual cpu it determines cpu
> frequency by reading the TSC, waits 1 second and reads the TSC again.
> To finish the 1 second wait it depends on the xen clock to tick.

Along with the serial log, guest dom0 output, could you also give the host grub 
.conf, guest grub.conf and the hvm guest config file?

Jimmy



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