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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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.

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