Re: [Xen-devel] PCI Passthrough ARM Design : Draft1

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 11 Jun 2015, Ian Campbell wrote:
> On Thu, 2015-06-11 at 07:25 -0400, Julien Grall wrote:
> > Hi Ian,
> > 
> > On 11/06/2015 04:56, Ian Campbell wrote:
> > > On Wed, 2015-06-10 at 15:21 -0400, Julien Grall wrote:
> > >> Hi,
> > >>
> > >> On 10/06/2015 08:45, Ian Campbell wrote:
> > >>>> 4. DomU access / assignment PCI device
> > >>>> --------------------------------------
> > >>>> When a device is attached to a domU, provision has to be made such that
> > >>>> it can
> > >>>> access the MMIO space of the device and xen is able to identify the 
> > >>>> mapping
> > >>>> between guest bdf and system bdf. Two hypercalls are introduced
> > >>>
> > >>> I don't think we want/need new hypercalls here, the same existing
> > >>> hypercalls which are used on x86 should be suitable. That's
> > >>> XEN_DOMCTL_memory_mapping from the toolstack I think.
> > >>
> > >> XEN_DOMCTL_memory_mapping is done by QEMU for x86 HVM when the guest
> > >> (i.e hvmloader?) is writing in the PCI BAR.
> > >
> > > What about for x86 PV? I think it is done by the toolstack there, I
> > > don't know what pciback does with accesses to BAR registers.
> > 
> > XEN_DOMCTL_memory_mapping is only used to map memory in stage-2 page 
> > table. This is only used for auto-translated guest.
> > 
> > In the case of x86 PV, the page-table is managed by the guest. The only 
> > things to do is to give the MMIO permission to the guest in order to the 
> > let him use them. This is done at boot time in the toolstack.
> 
> Ah yes, makes sense.
> 
> Manish, this sort of thing and the constraints etc should be discussed
> in the doc please.
 
I think that the toolstack (libxl) will need to call
xc_domain_memory_mapping (XEN_DOMCTL_memory_mapping), in addition to
xc_domain_iomem_permission, for auto-translated PV guests on x86 (PVH)
and ARM guests.

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