Re: [Xen-devel] [PATCH 09/28] ARM: GICv3 ITS: map device and LPIs to the ITS on physdev_op hypercall

[Julien Grall <julien.grall@xxxxxxx>]

On 01/03/17 19:42, Shanker Donthineni wrote:
> Hi Julien,
Hi Shanker,

> On 02/28/2017 12:29 PM, Julien Grall wrote:
> > On 27/02/17 17:20, Andre Przywara wrote:
> Direct VLPI injection feature is included in GICv4 architecture. A new
> set of VLPI commands are introduced to map ITS vpend/vprop tables, ITTE
> setup, and maintenance operations for VLPIs. In case of direct VLPI
> injection, domU/dom0 LPI commands are mapped to VLPI commands. Some of
> these commands must be applied to a real ITS hardware whenever XEN
> receives the ITS commands during runtime.
>
>
> Any thought on this, how we are going to support a direct VLPI injection
> without prolongating dom0/domU ITS commands to hardware at runtime?
direct vLPI injection will indeed require to propagate commands. But as 
the host command queue is shared among multiple guest, we have to 
prevent a guest to overflow the host command queue and affecting other 
guests.
During the discussion for GICv3 ITS support in Xen, we looked at various 
solution (see the various design doc sent by Ian Campbell [1]) and the 
only suitable one for it was to decouple vITS and ITS. This is what 
Andre has implemented in this series.
I don't know yet how we can make things secure for direct vLPI 
injection. For the time being, I think we should focus to get GICv3 ITS 
supported as it is a requirement to get MSI supported.
Once this is done, we can think about integrating directly vLPI in the 
code. Feel free to start a new thread about this.
Cheers,

[1] https://xenbits.xen.org/people/ianc/vits/

--
Julien Grall

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