Re: [Xen-devel] Requesting a freeze exception for vm_event memory introspection helpers

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 07/13/2015 04:51 PM, Wei Liu wrote:
> On Mon, Jul 13, 2015 at 10:35:44AM +0300, Razvan Cojocaru wrote:
>> Hello,
>>
>> I'd like to ask for a freeze exception for the "vm_event memory
>> introspection helpers" series.
>>
>> [PATCH 1/3] xen/mem_access: Support for memory-content hiding
>> [PATCH 2/3] xen/vm_event: Support for guest-requested events
>> [PATCH 3/3] xen/vm_event: Deny register writes if refused by
>> vm_event reply
>>
>> All patches have been acked by at least one person (though patch 1 is
>> still under some discussion).
>>
>> 1. Benefits of the series making it in this release:
>>
>> * Probably the most important benefit is that 4.6 development has been
>> very open to refactoring vm_events, and patch 3/3 makes vm_events behave
>> in a consistent manner (all register-write vm_events are pre-write events).
>>
>> * There are 3rd parties interested in these features (Tamas, for
>> example, has already expressed interest in uses of patch 1/1).
>>
> 
> These aren't really good arguments for getting this in for 4.6. It would
> be easy for you and Tamas to carry three patches for a while.
> 
> What are the impact to end users (end users -- meaning either system
> administrator that sets up Xen and other developers who want to use the
> new interface you introduce)?  Does this series consist of the last
> missing pieces of a feature?

Not just missing pieces of a feature, the guest-requested (formerly
VMCALL) vm_event patch is crucial for memory introspection, and without
the first patch it's very difficult to resume monitoring Windows guests
that have been put in hybernate-mode (instead of powered off).

I don't follow the impact question, sorry. If an administrator doesn't
use these features, the impact (in terms of speed and resources) should
be next to nothing.

If a freeze exception for the whole series is not an option at this
point, would it be appropriate to just drop patches requiring more
review and get the more acked ones in?


Thanks,
Razvan

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