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

On 2014/10/31 16:20, Jan Beulich wrote:
On 31.10.14 at 07:21, <kevin.tian@xxxxxxxxx> wrote:
  From: Chen, Tiejun
Sent: Friday, October 31, 2014 1:41 PM
On 2014/10/30 17:20, Jan Beulich wrote:
Thinking about this some more, this odd universal hole punching in
the E820 is very likely to end up causing problems. Hence I think
this really should be optional behavior, with pass through of devices
associated with RMRRs failing if not used. (This ought to include
punching holes for _just_ the devices passed through to a guest
upon creation when the option is not enabled.)

Yeah, we had a similar discussion internal to add a parameter to force
reserving RMRR. In this case we can't create a VM if these ranges
conflict with anything. So what about this idea?

Adding a new parameter (e.g. 'check-passthrough') looks the right
approach. When the parameter is on, RMRR check/hole punch is
activated at VM creation. Otherwise we just keep existing behavior.

If user configures device pass-through at creation time, this parameter
will be set by default. If user wants the VM capable of device hot-plug,
an explicit parameter can be added in the config file to enforce RMRR
check at creation time.

Not exactly, I specifically described it slightly differently above. When
devices get passed through and the option is absent, holes should be
punched only for the RMRRs associated with those devices (i.e.
ideally none). Of course this means we'll need a way to associate
RMRRs with devices in the tool stack and hvmloader, i.e. the current
XENMEM_reserved_device_memory_map alone won't suffice.

Yeah, current hypercall just provide RMRR entries without that associated BDF. And especially, in some cases one range may be shared by multiple devices...

So anyway, let me be clear something here before we step next. Firstly I'm wondering if you will refine that patch to achieve our requirement by yourself since looks you'd like to maintain that patch, or I should do this? And of course we can walk another way, like xenstore as Yang suggested previously.


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