question on KVM run flow on Intel-VT

question on KVM run flow on Intel-VT

[MaJia]

Hi,

I am learning kvm + Intel-VT nowadays. Since I am rookie on both kvm and
Intel-VT, I got following questions about run flow of kvm on vmx.

I think the cpu is running in 'vmx non-root' mode when execution flow
reach 'vmx_vcpu_run' and the batch of 'asm code' take responsibility of
run guest on cpu.

My question is, when and where will the execution flow return to vmx root
mode?

Please give me some hint about this point or route me to some documents.

Thanks.
Bruce.

Re: question on KVM run flow on Intel-VT

[Bruce MaJia]

On Wed, Apr 22, 2009 at 08:55:49PM +0800, MaJia wrote:
> Hi,
> 
> I am learning kvm + Intel-VT nowadays. Since I am rookie on both kvm and
> Intel-VT, I got following questions about run flow of kvm on vmx.
> 
> I think the cpu is running in 'vmx non-root' mode when execution flow
> reach 'vmx_vcpu_run' and the batch of 'asm code' take responsibility of
> run guest on cpu.
> 
> My question is, when and where will the execution flow return to vmx root
> mode?

I may not clarify my question. I mean, when vmexit occur, which caused by
executing io instruction from guest, will the cpu switch to vmx root
mode? Will the cpu direct goto run 'handle_io' function?

When cpu running in vmx non-root mode, an interrupt occurs, what is the
behavior of cpu?

Thanks.
Bruce.

> 
> Please give me some hint about this point or route me to some documents.
> 
> Thanks.
> Bruce.

Re: question on KVM run flow on Intel-VT

[Gregory Haskins]

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Hi Bruce,

Bruce MaJia wrote:
> On Wed, Apr 22, 2009 at 08:55:49PM +0800, MaJia wrote:
>   
>> Hi,
>>
>> I am learning kvm + Intel-VT nowadays. Since I am rookie on both kvm and
>> Intel-VT, I got following questions about run flow of kvm on vmx.
>>     

The Intel Software Developers Manual, Volume 3B, Chapter 21 is your
friend :)

http://download.intel.com/design/processor/manuals/253669.pdf

HTH,
-Greg



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Re: question on KVM run flow on Intel-VT

[Bruce MaJia]

Hi Greg,

On Wed, Apr 22, 2009 at 10:05:23AM -0400, Gregory Haskins wrote:
> Hi Bruce,
> 
> Bruce MaJia wrote:
> > On Wed, Apr 22, 2009 at 08:55:49PM +0800, MaJia wrote:
> >   
> >> Hi,
> >>
> >> I am learning kvm + Intel-VT nowadays. Since I am rookie on both kvm and
> >> Intel-VT, I got following questions about run flow of kvm on vmx.
> >>     
> 
> The Intel Software Developers Manual, Volume 3B, Chapter 21 is your
> friend :)
> 
> http://download.intel.com/design/processor/manuals/253669.pdf

Thanks for your response.

I actually take a quick glance at the Ch21 of Vol3B. I can found a list
in the chapter about 'xxx instruction will cause' vmexit and 'xxx will
cause vmexit if reg.xyz == abc' or 'xxx will not cause vmexit on
condition zzz'. But I could not find some clarification about:

? What is the cpu mode when vmexit occur.
? What is the behavior of cpu.
? Will it fetch next instruction from fixed phy addr?
? Or will it read next instruction from according vmcs?
? Or the cpu will just follow the standard process to handle
interrupt/exception?

Maybe I went too fast and miss some important information. Will you
speard a few words to guide me to correct point? Thanks in advance.

Bruce.

> 
> HTH,
> -Greg
> 
>