Re: [Xen-devel] [v7][RFC][PATCH 06/13] hvmloader/ram: check if guest memory is out of reserved device memory maps

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.11.14 at 06:05, <tiejun.chen@xxxxxxxxx> wrote:
> On 2014/11/3 20:34, Jan Beulich wrote:
>>>>> On 03.11.14 at 12:58, <tiejun.chen@xxxxxxxxx> wrote:
>>> Firstly we have a rule that we just allow all devices associated one
>>> RMRR to be assign same VM, right? So I mean while we create VM, we
>>> always call current hypercall but inside hypercall, Xen can know which
>>> devices will be assigned to this VM.
>>
>> I.e. the hypercall (at least optionally) becomes per-domain rather
>> than global. And you imply that device assignment happens
>> before memory getting populated (which likely can be arranged
> 
> I tried to find a clue about this point but unfortunately I can't trace 
> when we assign device exactly. But in theory, based on your hint I 
> prefer the device assignment should follow memory getting populated. 
> Because when we add a device, we need to create iommu map so this means 
> at this moment the guest should already finish populating memory, right?

There's no such strong connection: When a device gets assigned,
IOMMU mappings get created for all memory the guest already has
assigned (which at least in theory can include the "none" case).
When (more) memory gets assigned after a device was already
assigned to the guest, the IOMMU mappings would simply get
updated.

While I think you're right in that memory assignment happens
before device assignment, for your specific purpose it might have
been easier the other way around, since when memory gets
populated first you'll need special peeking into which devices will
get assigned later in order to avoid the respective RMRR areas,
or you'll need to modify device assignment code to move the
RAM populated there out of the way.

Jan


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