From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f171.google.com (mail-pd0-f171.google.com [209.85.192.171]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 8354F2C00B9 for ; Fri, 6 Sep 2013 20:45:38 +1000 (EST) Received: by mail-pd0-f171.google.com with SMTP id g10so3091350pdj.16 for ; Fri, 06 Sep 2013 03:45:36 -0700 (PDT) Message-ID: <5229B248.7030002@ozlabs.ru> Date: Fri, 06 Sep 2013 20:45:28 +1000 From: Alexey Kardashevskiy MIME-Version: 1.0 To: Gleb Natapov Subject: Re: [PATCH v9 12/13] KVM: PPC: Add support for IOMMU in-kernel handling References: <1377679070-3515-1-git-send-email-aik@ozlabs.ru> <1377679841-3822-1-git-send-email-aik@ozlabs.ru> <20130901120609.GJ22899@redhat.com> <52240295.7050608@ozlabs.ru> <20130903105315.GY22899@redhat.com> <1378353909.4321.126.camel@pasglop> <20130906065715.GG13021@redhat.com> In-Reply-To: <20130906065715.GG13021@redhat.com> Content-Type: text/plain; charset=KOI8-R Cc: kvm@vger.kernel.org, Alexander Graf , kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Paul Mackerras , Paolo Bonzini , linuxppc-dev@lists.ozlabs.org, David Gibson List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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