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

>>> On 18.01.16 at 17:33, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 18/01/16 16:27, Jan Beulich wrote:
>>>>> On 18.01.16 at 17:10, <andrew.cooper3@xxxxxxxxxx> 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.

Which is a reasonable requirement to enforce imo.


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