Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure

[Alexander Graf]

On 13.03.2012, at 06:07, David Gibson wrote:

> On Fri, Mar 09, 2012 at 11:23:01AM +0100, Paolo Bonzini wrote:
>> Il 09/03/2012 06:01, David Gibson ha scritto:
>>> This patch adds the basic infrastructure necessary to emulate an IOMMU
>>> visible to the guest.  The DMAContext structure is extended with
>>> information and a callback describing the translation, and the various
>>> DMA functions used by devices will now perform IOMMU translation using
>>> this callback.
>>> 
>>> Cc: Michael S. Tsirkin <address@hidden>
>>> Cc: Richard Henderson <address@hidden>
>>> 
>>> Signed-off-by: Eduard - Gabriel Munteanu <address@hidden>
>>> Signed-off-by: David Gibson <address@hidden>
>>> ---
>>> configure     |   12 ++++
>>> dma-helpers.c |  191 
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> dma.h         |  125 +++++++++++++++++++++++++++++++-------
>>> 3 files changed, 306 insertions(+), 22 deletions(-)
>>> 
>>> diff --git a/configure b/configure
>>> index a5eb832..e6fba2f 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -138,6 +138,7 @@ linux_aio=""
>>> cap_ng=""
>>> attr=""
>>> libattr=""
>>> +iommu="yes"
>>> xfs=""
>>> 
>>> vhost_net="no"
>>> @@ -784,6 +785,10 @@ for opt do
>>>   ;;
>>>   --enable-vhost-net) vhost_net="yes"
>>>   ;;
>>> +  --enable-iommu) iommu="yes"
>>> +  ;;
>>> +  --disable-iommu) iommu="no"
>>> +  ;;
>> 
>> This need not be a configure option.  Just enable it, or it will
>> bitrot.
> 
> I did wonder about that.  I'd like to hear that suggested by more than
> one person before I unconditionally add code which will impose an
> overhead on all emulated DMAs.

Maybe make it a target option? That way targets that want and need an IOMMU can 
compile the code in, while the others don't see performance hits. That would of 
course mean that we'd still have conditional code paths, but at least they 
wouldn't bitrot, as building multiple targets means you'd build both paths.


Alex