Re: [PATCH 1/2] docs/designs/launch: hyperlaunch design document

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Mar 25, 2021, at 8:32 AM, Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
> 
> On Wed, Mar 24, 2021 at 05:53:26AM -0700, Christopher Clark wrote:
>> On Wed, Mar 24, 2021 at 1:01 AM Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>>> 
>>> On Tue, Mar 23, 2021 at 10:39:53AM -0700, Christopher Clark wrote:
>>>> On Thu, Mar 18, 2021 at 9:43 AM Roger Pau Monné <roger.pau@xxxxxxxxxx> 
>>>> wrote:
>>> If you offload domain creation of guests with
>>> pci-passthrough devices to a control domain and/or hardware domain,
>>> I'm not sure I see the difference from normal domain creation, ie:
>>> it's no longer something specific to hyperlaunch, as I could achieve
>>> the same by using the existing xendomains init script.
>> 
>> So that's not what we've proposed, and hopefully not what we'll need to do.
>> 
>> Do you know if there is a need to perform work to support the
>> assignment of PCI devices at the point of domain creation (ie. in
>> domain_create), rather than handling it in a later step of domain
>> configuration, prior to the domain being started?
> 
> So while I think you could indeed create a domain from the hypervisor
> in a paused state and attach the pci devices later from a
> control/hardware domain, I don't see much benefit in doing it. If you
> need to end up waiting for a control/hardware domain to attach the
> devices and unpause you might as well do the whole domain creation
> from such control/hardware domain.

My understanding was that one of the primary advantages of domB was that you 
could compile and run arbitrary code in whatever language you wanted to, using 
already known tools.  If *all* we want to do is to assign some pre-defined 
specific BDFs to specific domains, then sure, we could add that capability to 
Xen.  But suppose you wanted to have the flexibility to handle changes in 
hardware at boot time?  “Scan through the PCI bus and assign anything that 
looks like a network card to domNet, and anything that looks like a USB 
controller to domUSB” is something you could easily do in domB, but would be 
way too complicated to add to Xen.

 -George