Re: [PATCH 04/14] hw/i386/vmport: Introduce vmx-version property

[Liran Alon]

On 10/03/2020 13:18, Michael S. Tsirkin wrote:
> On Tue, Mar 10, 2020 at 01:05:02PM +0200, Liran Alon wrote:
> > On 10/03/2020 11:32, Michael S. Tsirkin wrote:
> > > On Tue, Mar 10, 2020 at 01:54:01AM +0200, Liran Alon wrote:
> > > > Instead of hard-coding the VMX version, make it a VMPORT object property.
> > > > This would allow user to control it's value via "-global vmport.vmx-version=X".
> > > >
> > > > Reviewed-by: Nikita Leshenko <address@hidden>
> > > > Signed-off-by: Liran Alon <address@hidden>
> > > More detail on why this is useful?
> > It's more useful than returning a hard-coded "6" as the vmx-version...
>
> Maybe default should be 6 (a bit of explanation why 6 could be nice).
The default is indeed defined as 6. As it was before this patch.
There is not much to explain besides the fact that recent VMware 
products returns 6 here.

I don't recall any mapping between the returned version here and the 
supported set of VMPort commands. There is a separate mechanism (which 
we implement in another patch) to signal that a command is unsupported / 
failed.

The term "vmx-version" refers to the version of the Userspace-VMM of 
VMware which is called (confusingly) "vmx".

> > We have used it to preserve compatibility for some VMware guests that we run
> > as-is on top of QEMU/KVM which expects specific vmx-version or else they
> > fail to run properly.
> >
> > -Liran
> Any detail on which guest it is?
I will need to dig in production history to find it... They are usually 
proprietary appliances specially made to run as VMware VMs.
> Pretending to be a very advanced version has its pitfalls if we
> then don't behave the way vmware does, right?
In all those cases, we have taken the version number backwards, not forward.
> Figuring out the version number is I suspect a bit much to ask of users.
Most users will indeed not need to touch this. This is for advanced 
users, such as Ravello.
We usually figured this out by reverse-engineering the failed guest 
and/or examining the original VMware environment it used to run on.

-Liran