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Re: [Xen-devel] [RFC PATCH 5/23] Tools/libxc: Add viommu operations in libxc

On 2017年05月11日 20:35, Wei Liu wrote:
> On Mon, Apr 17, 2017 at 08:01:56PM +0800, Lan Tianyu wrote:
>> On 2017年04月17日 19:08, Wei Liu wrote:
>>> On Fri, Apr 14, 2017 at 11:38:15PM +0800, Lan, Tianyu wrote:
>>>> Hi Paul:
>>>>    Sorry for later response.
>>>> On 3/31/2017 3:57 AM, Chao Gao wrote:
>>>>> On Wed, Mar 29, 2017 at 09:08:06AM +0000, Paul Durrant wrote:
>>>>>>> -----Original Message-----
>>>>>>> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
>>>>>>> Chao Gao
>>>>>>> Sent: 29 March 2017 01:40
>>>>>>> To: Wei Liu <wei.liu2@xxxxxxxxxx>
>>>>>>> Cc: Lan Tianyu <tianyu.lan@xxxxxxxxx>; Kevin Tian 
>>>>>>> <kevin.tian@xxxxxxxxx>;
>>>>>>> Ian Jackson <Ian.Jackson@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxx
>>>>>>> Subject: Re: [Xen-devel] [RFC PATCH 5/23] Tools/libxc: Add viommu
>>>>>>> operations in libxc
>>>>>>> Tianyu is on vacation this two weeks, so I will try to address
>>>>>>> some comments on this series.
>>>>>>> On Tue, Mar 28, 2017 at 05:24:03PM +0100, Wei Liu wrote:
>>>>>>>> On Fri, Mar 17, 2017 at 07:27:05PM +0800, Lan Tianyu wrote:
>>>>>>>>> From: Chao Gao <chao.gao@xxxxxxxxx>
>>>>>>>>> In previous patch, we introduce a common vIOMMU layer. In our design,
>>>>>>>>> we create/destroy vIOMMU through DMOP interface instead of creating
>>>>>>> it
>>>>>>>>> according to a config flag of domain. It makes it is possible
>>>>>>>>> to create vIOMMU in device model or in tool stack.
>>>>>> I've not been following this closely so apologies if this has already 
>>>>>> been asked...
>>>>>> Why would you need to create a vIOMMU instance in an external device 
>>>>>> model.
>>>>>> Since the toolstack should be in control of the device model 
>>>>>> configuration why would it not know in advance that one was required?
>>>>> I assume your question is why we don't create a vIOMMU instance via 
>>>>> hypercall in toolstack.
>>>>> I think creating in toolstack is also ok and is easier to be reused by 
>>>>> pvh.
>>>>> If Tianyu has no concern about this, will move this part to toolstack.
>>>> We can move create/destroy vIOMMU in the tool stack but we still need to 
>>>> add
>>>> such dummy vIOMMU device model in Qemu to pass virtual device's DMA request
>>>> into Xen hypervisor. Qemu is required to use DMOP hypercall and tool stack
>>>> may use domctl hyercall. vIOMMU hypercalls will be divided into two part.
>>>> Domctl:
>>>>    create, destroy and query.
>>>> DMOP:
>>>>    vDev's DMA related operations.
>>>> Is this OK?
>>> Why are they divided into two libraries? Can't they be in DMOP at the
>>> same time?
>> Yes, we can use DMOP for all vIOMMU hyercalls if it's necessary to keep
>> unified vIOMMU hyercall type. In theory, DMOP dedicates to be used by
>> Qemu but we also can use it in tool stack. If we move create, destroy
>> and query operation to tool stack, it isn't necessary to use DMOP for
>> them since only tool stack will call them. This is why I said we could
>> use domctl for these operations. Both two ways will not affect function
>> implementation. Which one it's better from your view? :)
> After reading the subthread I think I agree with Paul. I.e. please
> separate them.

Sure. Will update.

Best regards
Tianyu Lan

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