Re: [Xen-devel] [PATCH v2 1/3] Add vmware_hw to xl.cfg

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.09.14 at 17:16, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 09/08/2014 10:21 AM, Jan Beulich wrote:
>>>>> On 08.09.14 at 15:56, <dslutz@xxxxxxxxxxx> wrote:
>>> On 09/08/14 09:20, Ian Campbell wrote:
>>>> On Wed, 2014-09-03 at 08:45 +0100, Jan Beulich wrote:
>>>>>>>> On 02.09.14 at 20:24, <dslutz@xxxxxxxxxxx> wrote:
>>>>>> On 09/02/14 03:28, Jan Beulich wrote:
>>>>>>>>>> On 01.09.14 at 17:33, <dslutz@xxxxxxxxxxx> wrote:
>>>>>>>> So based on this, I picked the order:
>>>>>>>>
>>>>>>>> 0x40000000 is viridian, vmware or xen
>>>>>>>> 0x40000100 is vmware or xen
>>>>>>>> 0x40000200 is xen
>>>>>>> Is there really a point in enabling both Viridian and VMware extensions
>>>>>>> at the same time?
>>>>>> Not that I know of (and I do not want to say there there is no code
>>>>>> out there that can work with both).  Instead of an error or warning
>>>>>> I went with what xen is currently doing and that seabios was happy
>>>>>> to find xen at 0x40000200.
>>>>>>
>>>>>> If the consensus is to ignore, or report an error or warning I will go 
>>>>>> that
>>>>>> way.  For now I am not planning on changing.
>>>>> My personal take on this is that the hypervisor (or perhaps already
>>>>> the tools) should reject enabling both at the same time.
>>>> That sounds sensible to me.
>>>>
>>>> Generally we seem to have the hypervisor check these things as a
>>>> backstop, to stop broken tools, but also check in the tools so we can
>>>> give a better error message.
>>>>
>>> Ok, with 2 votes this way how about (for v4) I will drop the change to
>>> xen/arch/x86/traps.c (I.E. 0x40000100 will be xen)  And change
>>>
>>> cpuid_vmware_leaves to return 0 if is_viridian_domain().
>> Not exactly - the conclusion rather is to not allow both to become
>> true at the same time.
> 
> I have vague recollection of some Windows products (newer Microsoft 
> Server releases?) expecting to run on hypervisor, i.e. Viridian. Would 
> such restriction break these?
> 
> Or is this orthogonal to this discussion (assuming I am right about MS 
> in the first place)?

The question is whether Windows, when run on VMware, makes use
of the VMware extensions _and_ after being migrated to Xen would
be capable of making use of the Viridian ones. I doubt that, i.e. I'd
assume that until rebooted they'd continue to use VMware's (with
the wild assumption that such a "live" migration is actually possible in
the first place), and they'd prefer using Viridian's after reboot. The
only dependency might be on devices that shouldn't disappear, but
that's independent of the hypervisor side foreign VMM emulation
afaict.

Jan


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