Re: [PATCH] virtio-balloon spec: provide a version of the "silentdeflate" feature that works

From: Michael S. Tsirkin
Date: Fri Sep 07 2012 - 06:42:44 EST


On Fri, Sep 07, 2012 at 04:09:50PM +0930, Rusty Russell wrote:
> > So it looks like a bug: we should teach driver to tell host first on leak?
> > Yan, Vadim, can you comment please?
> >
> > Also if true, looks like this bit will be useful to detect a fixed driver on
> > the hypervisor side - to avoid unmapping such pages? Rusty what do you
> > think?
>
> So, feature is unimplemented in qemu, and broken in drivers. I starting
> to share Paolo's dislike of it.

What is broken in drivers?

To me it looks like it works exactly as advertized: linux and bsd ack
TELL_HOST and tells host first. windows does not do either. Do windows
drivers currently are not broken: they just do not support the feature.

The claim that drivers and hyprevisors do not support it is false:
qemu does not support it but drivers do and in non trivial way.

> Don't understand why we'd care about fixed drivers though, if we remove
> the feature bit....
>
> Cheers,
> Rusty.

Do we really know there are no hypervisors implementing it?
As I said above drivers do have support.

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