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

[David Gibson <dgibson@redhat.com>]

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On Fri, 2 Sep 2016 14:18:47 +0800
Peter Xu <peterx@redhat.com> wrote:

> On Fri, Sep 02, 2016 at 02:15:57PM +0800, Peter Xu wrote:
> > > 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.  
> > 
> > But for vhost cases, we do not need CM bit enabled. That might be the
> > difference?
> > 
> > I think we need to have vhost working even without CM bit. Device
> > IOTLB should be able to achieve that.  
> 
> The problem is that, IMHO we should be very careful on enabling CM
> bit. After enabling it, system might get slower (though I haven't
> tried it yet), or even very slow? So maybe we will only enable it when
> really needed (e.g., to do device passthrough and build the shadow
> table).

Um.. what's the CM bit and what does it have to do with anything?

-- 
David Gibson <dgibson@redhat.com>
Senior Software Engineer, Virtualization, Red Hat

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