On 09/06/2013 04:57 PM, Gleb Natapov wrote: > On Thu, Sep 05, 2013 at 02:05:09PM +1000, Benjamin Herrenschmidt wrote: >> On Tue, 2013-09-03 at 13:53 +0300, Gleb Natapov wrote: >>>> Or supporting all IOMMU links (and leaving emulated stuff as is) in on >>>> "device" is the last thing I have to do and then you'll ack the patch? >>>> >>> I am concerned more about API here. Internal implementation details I >>> leave to powerpc experts :) >> >> So Gleb, I want to step in for a bit here. >> >> While I understand that the new KVM device API is all nice and shiny and that this >> whole thing should probably have been KVM devices in the first place (had they >> existed or had we been told back then), the point is, the API for handling >> HW IOMMUs that Alexey is trying to add is an extension of an existing mechanism >> used for emulated IOMMUs. >> >> The internal data structure is shared, and fundamentally, by forcing him to >> use that new KVM device for the "new stuff", we create a oddball API with >> an ioctl for one type of iommu and a KVM device for the other, which makes >> the implementation a complete mess in the kernel (and you should care :-) >> > Is it unfixable mess? Even if Alexey will do what you suggested earlier? > > - Convert *both* existing TCE objects to the new > KVM_CREATE_DEVICE, and have some backward compat code for the old one. > > The point is implementation usually can be changed, but for API it is > much harder to do so. > >> So for something completely new, I would tend to agree with you. However, I >> still think that for this specific case, we should just plonk-in the original >> ioctl proposed by Alexey and be done with it. >> > Do you think this is the last extension to IOMMU code, or we will see > more and will use same justification to continue adding ioctls? Ok. I give up :) I implemented KVM device the way you suggested. Could you please have a look? It is "[PATCH v10 12/13] KVM: PPC: Add support for IOMMU in-kernel handling", attached to this thread. Thanks! -- Alexey -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>