On Tue, Aug 14, 2012 at 11:49:06PM +0300, Michael S. Tsirkin wrote:

On Tue, Aug 14, 2012 at 05:29:50PM -0300, Rafael Aquini wrote:

quoted

On Tue, Aug 14, 2012 at 11:24:01PM +0300, Michael S. Tsirkin wrote:

quoted

On Tue, Aug 14, 2012 at 05:08:31PM -0300, Rafael Aquini wrote:

quoted

On Tue, Aug 14, 2012 at 10:59:16PM +0300, Michael S. Tsirkin wrote:

quoted

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What if there is more than one balloon device?

Is it possible to load this driver twice, or are you foreseeing a future case
where this driver will be able to manage several distinct memory balloons for
the same guest?

Second.
It is easy to create several balloons they are just
pci devices.

 


and it might not be too important to make it work but
at least would be nice not to have a crash in this
setup.

Fair enough. For now, as I believe it's safe to assume we are only inflating one
balloon per guest, I'd like to propose this as a future enhancement. Sounds
good?
 

Since guest crashes when it's not the case, no it doesn't, sorry :(.

Ok, but right now this driver only takes care of 1 balloon per guest,

It does? Are you sure? There is no global state as far as I can see. So
I can create 2 devices and driver will happily create two instances,
each one can be inflated/deflated independently.

quoted

so how
could this approach crash it? 

Add device. inflate. Add another device. inflate. deflate. unplug.
Now you have pointer to freed memory and when mm touches
page from first device, you ge use after free.

quoted

Your point is a good thing to be on a to-do list for future enhancements, but
it's not a dealbreaker for the present balloon driver implementation, IMHO.

Yes it looks like a dealbreaker to me.

To clarify, the global state that this patch adds, is ugly
even if we didn't support multiple balloons yet.
So I don't think I can accept such a patch.
Rusty has a final word here, maybe he thinks differently.

-- 
MST 

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