Re: [Xen-devel] [PATCH 02/16] SUPPORT.md: Add core functionality

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.11.17 at 11:36, <george.dunlap@xxxxxxxxxx> wrote:
> On 11/21/2017 08:03 AM, Jan Beulich wrote:
>>>>> On 13.11.17 at 16:41, <george.dunlap@xxxxxxxxxx> wrote:
>>> --- a/SUPPORT.md
>>> +++ b/SUPPORT.md
>>> @@ -16,6 +16,65 @@ for the definitions of the support status levels etc.
>>>  
>>>  # Feature Support
>>>  
>>> +## Memory Management
>>> +
>>> +### Memory Ballooning
>>> +
>>> +    Status: Supported
>> 
>> Is this a proper feature in the context we're talking about? To me
>> it's meaningful in guest OS context only. I also wouldn't really
>> consider it "core", but placement within the series clearly is a minor
>> aspect.
>> 
>> I'd prefer this to be dropped altogether as a feature, but
> 
> This doesn't make any sense to me.  Allowing a guest to modify its own
> memory requires a *lot* of support, spread throughout the hypervisor;
> and there are a huge number of recent security holes that would have
> been much more difficult to exploit if guests didn't have the ability to
> balloon up or down.
> 
> If what you mean is *specifically* the technique of making a "memory
> balloon" to trick the guest OS into handing back memory without knowing
> it, then it's just a matter of semantics.  We could call this "dynamic
> memory control" or something like that if you prefer (although we'd have
> to mention ballooning in the description to make sure people can find it).

Indeed I'd prefer the alternative naming: Outside of p2m-pod.c there's
no mention of the term "balloon" in any of the hypervisor source files.
Furthermore this "dynamic memory control" can be used for things other
than ballooning, all of which I think is (to be) supported.

Jan


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