Re: [RFC] event channels and xen callbacks

[Mathieu Ropert <mro@adviseo.fr>]

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