Oops! Since no one else is impacted by these offsets yet, I'd like to
reserve locations for the vmread and vmwrite bitmaps, used by
virtualized VMCS shadowing.
I know I've lost some credibility after the "save/restore nested
state" debacle, but I do intend to upstream support for virtualized
VMCS shadowing soon.
On Mon, Apr 30, 2018 at 2:48 PM, Jim Mattson <jmattson@xxxxxxxxxx> 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.
