Re: [Qemu-devel] [PATCH v5 15/18] intel_iommu: introduce IEC notifiers

[Jan Kiszka <jan.kiszka@web.de>]

On 2016-04-28 10:29, Peter Xu wrote:
> On Thu, Apr 28, 2016 at 09:26:01AM +0200, Jan Kiszka wrote:
>> On 2016-04-28 09:05, Peter Xu wrote:
>>> This patch introduces Intel VT-d IEC (Interrupt Entry Cache)
>>> invalidation notifier list. When vIOMMU receives IEC invalidate request,
>>> all the registered units will be notified with specific invalidation
>>> requests.
>>
>> This should be designed to be IOMMU-agnostic, i.e. become reusable for
>> the AMD implementation. I suspect we will have the same need for route
>> invalidations there as well...
> 
> Yes possibly...
> 
> I feel like there are lots of things that can be shared between
> Intel and AMD IOMMUs. I just do not know what is the most suitable
> "extent" that we should abstract these shared functionalities
> between the two, and how.

A rough indicator: if you add something that has "vtd" in its name to
non-vtd code, think twice about some reusable abstraction ;). So,
something like "vtd_get_iommu" could already be named and designed to
have two provides (e.g. allow an IOMMU to register itself as provider,
return that registered instance(s) when requested).

> 
> For example, AFAIU, a better solution for current IOMMU
> codes (including Intel and AMD) is to provide a common framework
> (like...  X86IOMMU?), abstract these shared things out into a
> framework, like per device name spaces, iotlb, IEC notifications,
> etc... However, that will need a lot of further work. Also, I still
> do not know whether this is a good idea even in the future.
> 
> So, will this be a good point that we start to think about common
> code blocks for both Intel and AMD IOMMU?

The core iommu code can still be refactored later on. I'm now more
concerned about the hooks you add to generic code, see above.

Jan