Re: [PATCH v5 09/15] vtd: add lookup_page method to iommu_ops

From: Paul Durrant <Paul.Durrant@citrix.com>
To: Kevin Tian <kevin.tian@intel.com>, Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	George Dunlap <George.Dunlap@citrix.com>
Subject: Re: [PATCH v5 09/15] vtd: add lookup_page method to iommu_ops
Date: Tue, 7 Aug 2018 08:37:07 +0000	[thread overview]
Message-ID: <2a55d245b9854e4dbc5eb8b65706fd9f@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <AADFC41AFE54684AB9EE6CBC0274A5D1912AE997@SHSMSX101.ccr.corp.intel.com>

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@intel.com]
> Sent: 07 August 2018 09:33
> To: Jan Beulich <JBeulich@suse.com>; Paul Durrant
> <Paul.Durrant@citrix.com>
> Cc: George Dunlap <George.Dunlap@citrix.com>; xen-devel <xen-
> devel@lists.xenproject.org>
> Subject: RE: [PATCH v5 09/15] vtd: add lookup_page method to iommu_ops
> 
> > From: Jan Beulich [mailto:JBeulich@suse.com]
> > Sent: Tuesday, August 7, 2018 4:30 PM
> >
> > >>> On 07.08.18 at 10:21, <Paul.Durrant@citrix.com> wrote:
> > >> From: Tian, Kevin [mailto:kevin.tian@intel.com]
> > >> Sent: 07 August 2018 04:25
> > >>
> > >> > From: Paul Durrant [mailto:paul.durrant@citrix.com]
> > >> > Sent: Saturday, August 4, 2018 1:22 AM
> > >> >
> > >> > --- a/xen/drivers/passthrough/vtd/iommu.c
> > >> > +++ b/xen/drivers/passthrough/vtd/iommu.c
> > >> > @@ -1830,6 +1830,39 @@ static int __must_check
> > >> > intel_iommu_unmap_page(struct domain *d,
> > >> >      return dma_pte_clear_one(d, bfn_to_baddr(bfn));
> > >> >  }
> > >> >
> > >> > +static int intel_iommu_lookup_page(struct domain *d, bfn_t bfn,
> > mfn_t
> > >> > *mfn,
> > >> > +                                   unsigned int *flags)
> > >>
> > >> Not looking at later patches yet... but in concept bfn address
> > >> space is per device instead of per domain.
> > >
> > > Not in this case. Xen has always maintained a single IOMMU address per
> > > virtual machine. That is what BFN refers to.
> >
> > Nut is that a model we can maintain mid and long term? In particular
> > on ARM, where Julien has told me a single system could have multiple
> > _different_ IOMMUs, I could easily see the address spaces diverging.
> >
> 
> multiple IOMMUs is another thing.
> 
> what I questioned is that even one IOMMU needs to support mulitiple
> address spaces. That is the point of an IOMMU...

Indeed and that is why we use it to enforce domain separation. I see no need, as yet, to enforce separation within a domain. That need may arise later and the code can be modified at that point.

  Paul

> 
> Thanks
> Kevin

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