Re: [PATCH v3 4/4] x86/PV: enable the emulated PIT

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 18/01/16 16:27, Jan Beulich wrote:
>>>> On 18.01.16 at 17:10, <andrew.cooper3@citrix.com> wrote:
>> On 18/01/16 11:06, Jan Beulich wrote:
>>>> Whatever (eventually) gets used to set these values will however be
>>>> present in the xl configuration, which is at the very start of the
>>>> stream, and is what is used to create the new domain.
>>> Which makes me repeat the question: Is this an inherent property
>>> or just "that's the way it is right now"? And then of course the
>>> question arises whether setting those flags at domain creation time
>>> is the right model. I.e. ...
>>>
>>>> We really don't want the libxc migrate code to be making the
>>>> DOMCTL_createdomain hypercall itself; it opens up a whole new attack
>>>> surface via cunningly-crafted save image.  The best we can do is have a
>>>> sanity check later on.
>>> ... what about deriving the emulation flags from the various
>>> pieces of state getting loaded, at least when there are matching
>>> pairs (which namely is the case for PIT)?
>> How would you suggest setting theses flags up in the plain domain build
>> case then?
> Via a specific (new) hypercall, along the lines of what
> XEN_DOMCTL_arm_configure_domain was?

This adds the existing problems we have between the createdomain and
max_cpus hypercalls.

We need to either specify all information in a single hypercall, or have
a dedicated construction phase, during which most hypercalls are invalid
to use.

(IMO - All domain construction is a rats nest in need of redesigning
from scratch.)

~Andrew