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Date: Fri, 11 Nov 2016 05:39:26 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable
 VTD_CAP_CM to vIOMMU capility exposoed to guest
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To: Jason Wang <jasowang@redhat.com>
Cc: "Aviv B.D" <bd.aviv@gmail.com>, qemu-devel@nongnu.org, Jan Kiszka <jan.kiszka@siemens.com>, Alex Williamson <alex.williamson@redhat.com>, Peter Xu <peterx@redhat.com>

On Fri, Nov 11, 2016 at 10:32:42AM +0800, Jason Wang wrote:
>=20
>=20
> On 2016=E5=B9=B411=E6=9C=8810=E6=97=A5 06:00, Michael S. Tsirkin wrote:
> > On Wed, Nov 09, 2016 at 03:28:02PM +0800, Jason Wang wrote:
> > > >
> > > >
> > > >On 2016=E5=B9=B411=E6=9C=8808=E6=97=A5 19:04, Aviv B.D wrote:
> > > > > >From: "Aviv Ben-David"<bd.aviv@gmail.com>
> > > > > >
> > > > > >This capability asks the guest to invalidate cache before each=
 map operation.
> > > > > >We can use this invalidation to trap map operations in the hyp=
ervisor.
> > > >
> > > >Hi:
> > > >
> > > >Like I've asked twice in the past, I want to know why don't you ca=
che
> > > >translation faults as what spec required (especially this is a gue=
st visible
> > > >behavior)?
> > > >
> > > >Btw, please cc me on posting future versions.
> > > >
> > > >Thanks
> > Caching isn't guest visible.
>=20
> Seems not, if one fault mapping were cached by IOTLB. Guest can notice =
this
> behavior.

Sorry, I don't get what you are saying.

> > Spec just says you*can*  cache,
> > not that you must.
> >=20
>=20
> Yes, but what did in this patch is "don't". What I suggest is just a "c=
an",
> since anyway the IOTLB entries were limited and could be replaced by ot=
her.
>=20
> Thanks

Have trouble understanding this. Can you given an example of
a guest visible difference?