On Mon, Apr 30, 2018 at 02:48:34PM -0700, Jim Mattson wrote:
> On Mon, Apr 30, 2018 at 2:14 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On Fri, Apr 27, 2018 at 11:14:35AM -0700, Jim Mattson wrote:
> >> Changing the VMCS12 layout breaks save/restore compatibility with
> >> older kvm releases.
> >>
> >> Google has been saving/restoring nested VMX state based on the v4.0
> >> layout. There are no other known users of the
> >> KVM_{GET,SET}_NESTED_STATE ioctls, since those ioctls have not yet
> >> been accepted upstream.
> >
> > What is the advantage of that layout vs the one that is now? I vaguelly
> > recall something about it being quite bloated and the newer more sparse?
>
> The only differences between the v4.0 layout and today's layout is
> that four new fields have been intermingled in such a way that the old
> offsets have not been preserved. I'm suggesting that these four fields
> be moved so as to preserve the offsets of all of the pre-existing
> fields.
Could you roll that explanation in the commit please? Especially as the
'save/restore compatibility' is not exactly correct - as the old upstream
kvm releases at all don't work with this ...
