[PATCH 0/3] Architecture independence layer - v0

[Christian Ehrhardt <ehrhardt-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

Hello,
these three patches in v0 are be a base for discussion about an architecture
independence layer. It is part of an internal prototype we use to access 
the code
of our port as we develop it currently.
I know that a lot of things in the patches are still needing refining and
polishing, but it is enough to start the discussion about the basic 
mechanism
before I (or someone else) spend to much work working on such a layer.

The idea is, that x86 should always work however we split kvm internally to
generic/arch. The split in the current patches is done by gut feeling 
and will
improve by a) reviewing some functions more in detail, b) along the 
development
of our arch port and c) by your comments.

I know that the current kvm userspace is still very x86 centric and this 
will
(has to) change in the future, but we need an architecture mapping now 
to develop
our arch code. It should be adaptable to any userspace interface change 
that is coming.

Basics I used:
- Since architecture will not change at runtime I do not use a arch_ops 
structure
- Instead I used a hidden Kconfig value specifying the kvm architecture 
which then
  influence the make file to link together the generic and the arch 
specific part
  to one kvm module
- I split the code into kvm_main.c (generic) and kvm_x86.h/kvm_x86.c 
(arch portion)
- A new header kvm_arch.h specifies the interface the architecture has 
to implement
- The ioctl interfaces are implemented by the generic kvm_main.c in 
three ways
a) a completely generic function is covered by kvm_main.c completely
b) a completely arch dependent function is not covered in kvm_main.c - 
at the end
   each ioctl goes to a architecture mapping doing the rest of the ioctl 
not handled
   in the generic part e.g. in kvm_vcpu_ioctl:
        default:
               r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
        }
c) functions that have a significant amount of shared code are 
implemented by
   kvm_main.c using kvm_arch_* to implement the arch specific part. 
Either by just
   mapping the old *_ioctl_whatever to *_arch_whatever or by moving some 
more of the
   code out of the arch function up to the generic portion e.g.:
          case KVM_RUN:
                r = -EINVAL;
                if (arg)
                        goto out;
                r = kvm_arch_vcpu_run(vcpu, vcpu->run);
                break;
- there is still a lot of potential to move code up and down along these 
split, but
  thats it so far. I strive to improve that patch series until we are 
happy with it

The patch compiles and works without issues on my Opteron based machine 
here,
unfortunately I have no Intel base HW to test.
I look forward to every comment. Even if this approach may not be what 
we want in
the end, at least it starts the discussion how to do it :-)

Grüsse / Regards
Christian Ehrhardt

P.S. Still a todo and not (yet) covered in this patch proposal is the 
arch splitting of structures like vcpu to a generic and an arch part.

-- 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org
Ehrhardt-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org

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