Re: Cross vendor migration ideas

[Avi Kivity <avi@redhat.com>]

Glauber Costa wrote:
> We can possibly do it a little bit better by emulating in the guest directly.
> So the deal would be emulation both in the host and the guest. If the
> guest have it,
> fine. Otherwise, we use host emulation, that is slower, but works.
>   

If the guest is modifiable, this is easy.  Include both syscall and 
sysenter paths in the vsyscall page, with a jmp to select between them.  
If we trap a #UD pointing at a syscall or sysenter, emulate it, and 
patch the jmp instruction to point at the other path.  This way we have 
a self-adjusting syscall/sysenter entry point.  We also need to tell kvm 
not to emulate the instruction, so that the #UD actually reaches the kernel.

If the guest is not modifiable, this means patching.  This is much 
harder than tpr patching since we don't have any space to hide our code 
in.  Maybe we can reverse engineer the vsyscall page and hack it, but 
this may take a lot of work.

-- 
error compiling committee.c: too many arguments to function