Re: [Xen-devel] Hypercall interface changes for PAE

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 31 May 2005, at 21:38, Gerd Knorr wrote:

> I'd expect with a identical interface we'll only have to add a
> PAE-enabled domain builder to boot domU (there are multiple
> already anyway, right?), whereas with different interfaces the
> split goes down to the shared lib which provides the hypercall
> interface to the tools.
I don't think we want pae/non-pae builder made visible to higher-level 
tools. We can hide the auto-switch between builders within libxc 
itself. The same goes for domain save/restore code as well (although 
there is potentially scope for more binary-code sharing between 
pae/non-pae in this case).
> Point is I expect it being much easier to switch at runtime
> between pae and non-pae in the tools when the hypercall
> interface is identical.  I might be wrong on this though.
The code that would be affected by an interface difference is precisely 
that code which manipulates page tables, and so is already broken by 
the different pagetable format. The only way unmodified non-pae code 
could possibly be made to work is by using shadow page tables. In that 
case we would hook off the call to e.g., do_mmu_update() very early 
anyway (off into shadow code). Hardly different really from jumping in 
the first place at a different hypercall function with different 
prototype: this latter would arguably be cleaner and less cluttered, as 
well as easily allowing us to support non-pae hypercall interface 
within pae xen.
I really think that creating this interface inconsistency is not 
something to be worried about.
 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel