Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest

[Jason Wang]

On 2016年11月10日 06:00, Michael S. Tsirkin wrote:
> On Wed, Nov 09, 2016 at 03:28:02PM +0800, Jason Wang wrote:
> > >
> > >
> > >On 2016年11月08日 19:04, Aviv B.D wrote:
> > > > >From: "Aviv Ben-David"<address@hidden>
> > > > >
> > > > >This capability asks the guest to invalidate cache before each map operation.
> > > > >We can use this invalidation to trap map operations in the hypervisor.
> > >
> > >Hi:
> > >
> > >Like I've asked twice in the past, I want to know why don't you cache
> > >translation faults as what spec required (especially this is a guest visible
> > >behavior)?
> > >
> > >Btw, please cc me on posting future versions.
> > >
> > >Thanks
> Caching isn't guest visible.

Seems not, if one fault mapping were cached by IOTLB. Guest can notice 
this behavior.

> Spec just says you*can*  cache,
> not that you must.

Yes, but what did in this patch is "don't". What I suggest is just a 
"can", since anyway the IOTLB entries were limited and could be replaced 
by other.

Thanks