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

[Peter Xu]

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).

-- peterx