Re: [Xen-devel] [RFC] event channels and xen callbacks

[Mathieu Ropert <mro@xxxxxxxxxx>]

Keir Fraser wrote:

> On 4 Apr 2006, at 17:10, Mathieu Ropert wrote:
>
> > i'm currently playing a bit with event channels and hypervisor 
> > callbacks, and i find myself stuck because i miss some informations. 
> > Maybe you can give me some hints:
> > on amd64 arch, i'd like to know about hypervisor callback: ie, stack 
> > layout when
> > called by Xen, stack location in memory (is it using the TSS entry as 
> > hardware  traps do?) and finally, about how HYPERVISOR_iret() expects 
> > to find the stack upon call (like when you used iret? or something 
> > else?).
> > I may write a little paper or tutorial from i've learned and didn't 
> > found in Xen doc after i get a better view of the whole thing...
>
> 1. The stack layout on callback is just as for a native hardware 
> interrupt or exception. Those exceptions that push an error code when 
> running natively also do so when running on Xen, for example.
> 2. The TSS isn't fully virtualised by Xen -- instead you register your 
> kernel stack with the stack_switch() hypercall. Calling this is 
> equivalent to writing your stack pointer into your TSS when running 
> natively.
> 3. When calling HYPERVISOR_iret() there should be a iret_context 
> swtructure at the top of the stack. See its definition, and a big 
> comment, in xen/include/public/arch-x86_64.h.
>  -- Keir
Thanks Keir, that helped me a lot!


Regards,

Mathieu

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