lkml.org 
[lkml]   [2008]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC] CPUID usage for interaction between Hypervisors and Linux.
Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> And you're absolutely right that the guest may end up picking and
>> choosing different parts of the interfaces. That's how it is supposed
>> to work.
>
> No, that would be a horrible, horrible mistake. There's no sane way to
> implement that; it would mean that the hypervisor would have to have
> some kind of state model that incorporates all the ABIs in a consistent
> way. Any guest using multiple ABIs would effectively end up being
> dependent on a particular hypervisor via a frankensteinian interface
> that no other hypervisor would implement in the same way, even if they
> claim to implement the same set of interfaces.
>
> If the hypervisor just needs to deal with one at a time then it can have
> relatively simple ABI<->internal state translation.
>
> However, if you have the notion of hypervisor-agnostic or common
> interfaces, then you can include those as part of the rest of the ABI
> and make it sane (so Xen+common, hyperv+common, etc).
>

It depends on what classes of interfaces you're talking about. I think
you and Jun have a bit narrow definition of "ABI" in this context. This
is functionally equivalent to hardware interfaces (after all, that is
what the hypervisor ABI *is* as far as the kernel is concerned) -- noone
expects, say, a SATA controller that can run in legacy IDE mode to also
take AHCI commands at the same time, but the kernel *does* expect that a
chipset which exports LAPIC, HPET, PMTMR and TSC clock sources can use
all four at the same time. In the latter case the interfaces are
inherently independent and refer to different chunks of hardware which
just happen to be related in that they all are related to timing. In
the former case, we're dealing with *one* piece of hardware which can
operate in one of two modes.

For hypervisors, you will end up with cases where you have both types --
for example, KVM will happily use VMware's video interface, but that
doesn't mean KVM wants to use VMware's interfaces for storage. This is
exactly how it should be: the extent this kind of mix and match that is
possible is a matter of the definition of the individual interfaces
themselves, not of the overall architecture.

-hpa


\
 
 \ /
  Last update: 2008-10-08 03:17    [from the cache]
©2003-2011 Jasper Spaans