Xen Q35 & virtual VTD support

Xen Q35 & virtual VTD support

[Lan, Tianyu]

Hi All:	
We are researching how to add virtual VTD support for Xen HVM
guest. Current qemu has a basic virtual VTD support for Q35. I'd like to
confirm whether Xen supports Q35 or not. Can we reuse it for Xen? Thanks.

The motivations of adding virtual VTD support for Xen prepare for
1) Shared Virtual Memory (SVM)
2) Increase max VCPUs > 255 (The feature relies on virtual VTD irq
remapping function.)

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Re: Xen Q35 & virtual VTD support

[Stefano Stabellini]

Hello Tianyu,

I am CC'ing Anthony who should have a better idea about this. Also
please use my kernel.org email address for future correspondence.

What do you mean by reusing Q35 for Xen? If you mean using QEMU to
emulate a Q35 based machine for HVM guests, I think that should be OK.

Thanks,

Stefano


On Mon, 9 May 2016, Lan, Tianyu wrote:
> Hi All:	
> We are researching how to add virtual VTD support for Xen HVM
> guest. Current qemu has a basic virtual VTD support for Q35. I'd like to
> confirm whether Xen supports Q35 or not. Can we reuse it for Xen? Thanks.
> 
> The motivations of adding virtual VTD support for Xen prepare for
> 1) Shared Virtual Memory (SVM)
> 2) Increase max VCPUs > 255 (The feature relies on virtual VTD irq
> remapping function.)
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
> 

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Re: Xen Q35 & virtual VTD support

[Lan, Tianyu]

On 5/10/2016 6:11 PM, Stefano Stabellini wrote:
> Hello Tianyu,
>
> I am CC'ing Anthony who should have a better idea about this. Also
> please use my kernel.org email address for future correspondence.
>

OK. I get it.

> What do you mean by reusing Q35 for Xen? If you mean using QEMU to
> emulate a Q35 based machine for HVM guests, I think that should be OK.
>

 From xl code, I findit passes pc, xenpv or xenfv as "-machine" param
to Qemu except Q35. I also tried changing code to select Q35 in the xl
but guest didn't boot up. So I want to check whether Xen supports Q35 in
the current code or not.

If yes, we can reuse Qemu virtual VTD for Xen with minor changes.


> Thanks,
>
> Stefano
>
>
> On Mon, 9 May 2016, Lan, Tianyu wrote:
>> Hi All:	
>> We are researching how to add virtual VTD support for Xen HVM
>> guest. Current qemu has a basic virtual VTD support for Q35. I'd like to
>> confirm whether Xen supports Q35 or not. Can we reuse it for Xen? Thanks.
>>
>> The motivations of adding virtual VTD support for Xen prepare for
>> 1) Shared Virtual Memory (SVM)
>> 2) Increase max VCPUs > 255 (The feature relies on virtual VTD irq
>> remapping function.)
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel
>>

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Re: Xen Q35 & virtual VTD support

[Anthony PERARD]

On Tue, May 10, 2016 at 10:31:38PM +0800, Lan, Tianyu wrote:
> On 5/10/2016 6:11 PM, Stefano Stabellini wrote:
> > Hello Tianyu,
> > 
> > What do you mean by reusing Q35 for Xen? If you mean using QEMU to
> > emulate a Q35 based machine for HVM guests, I think that should be OK.
> > 
> 
> From xl code, I findit passes pc, xenpv or xenfv as "-machine" param
> to Qemu except Q35. I also tried changing code to select Q35 in the xl
> but guest didn't boot up. So I want to check whether Xen supports Q35 in
> the current code or not.

No, Xen do not support Q35.

But that is possible in the future, I did some work on it in the past, you
can find it here if you are curious:

http://xenbits.xen.org/gitweb/?p=people/aperard/xen-unstable.git;a=shortlog;h=refs/heads/machine-q35-wip

I'm not sure if it's going to help you.

-- 
Anthony PERARD

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Re: Xen Q35 & virtual VTD support

[Lan, Tianyu]

On 5/10/2016 10:52 PM, Anthony PERARD wrote:
> On Tue, May 10, 2016 at 10:31:38PM +0800, Lan, Tianyu wrote:
>> On 5/10/2016 6:11 PM, Stefano Stabellini wrote:
>>> Hello Tianyu,
>>>
>>> What do you mean by reusing Q35 for Xen? If you mean using QEMU to
>>> emulate a Q35 based machine for HVM guests, I think that should be OK.
>>>
>>
>> From xl code, I findit passes pc, xenpv or xenfv as "-machine" param
>> to Qemu except Q35. I also tried changing code to select Q35 in the xl
>> but guest didn't boot up. So I want to check whether Xen supports Q35 in
>> the current code or not.
>
> No, Xen do not support Q35.
>
> But that is possible in the future, I did some work on it in the past, you
> can find it here if you are curious:
>
> http://xenbits.xen.org/gitweb/?p=people/aperard/xen-unstable.git;a=shortlog;h=refs/heads/machine-q35-wip
>
> I'm not sure if it's going to help you.
>

Great. Thanks a lot for your help. BTW, do you have plan to upstream 
these patches?




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