Re: [Qemu-devel] [PATCH for 2.8 10/11] Revert "intel_iommu: Throw hw_error on notify_started"

[David Gibson]

On Fri, 2 Sep 2016 13:37:33 +0800
Peter Xu <address@hidden> wrote:

> On Fri, Sep 02, 2016 at 02:15:04PM +1000, David Gibson wrote:
> > What!?  I see no reason you need a different notifier, just fix the
> > implementation of the current one.  As a bonus this will also give you
> > working VFIO passthrough with vIOMMU on x86, something which should
> > work already, but doesn't.  
> 
> Hi, David,
> 
> Do you mean that we can enhance the interface to suite the two needs?
> E.g., adding a "IOTLB notification type" definition:
> 
> - "full": for those who is listening on all mapping changes including
>   additions (VFIO use case)
> 
> - "cache_only": for those who only cares about cache invalidations
>   (device IOTLB, aka, vhost use case)
> 
> We can:
> 
> - add notify type when we register the notifiers (e.g., when VFIO
>   registers IOMMU notifier, it should specify the type as "full", so
>   it won't receive notification if it's device IOTLB invalidations).
> 
> - pass this type when trigger the notification, so for each IOMMU
>   notify handler, it can selectively disgard the notification.
> 
> Not sure whether above makes sense.

No, implement the full notifier, and a listener which only wants the
invalidates can just ignore callbacks which add new mappings.

As I said, you'll need this to get VFIO working with vIOMMU which
someone is bound to want soon enough anyway.

-- 
David Gibson <address@hidden>
Senior Software Engineer, Virtualization, Red Hat

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