linux-kernel - Re: [PATCH] virtio-balloon spec: provide a version of the "silent deflate" feature that works

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Date:	Fri, 7 Sep 2012 13:43:06 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, fes@...gle.com,
	aarcange@...hat.com, riel@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mikew@...gle.com, yinghan@...gle.com,
	virtualization@...ts.linux-foundation.org, yvugenfi@...hat.com,
	vrozenfe@...hat.com
Subject: Re: [PATCH] virtio-balloon spec: provide a version of the "silent
 deflate" feature that works

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.

-- 
MST
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