Xen devel - Feb 2010 - [help] rsp in case of interrupt/exception in ring0

Hi,

can someone help me understand this.

When a cpu is in hyp code and int/exception comes in, how/where is rsp 
saved? According to intel manual if there''s no ring transition, then
the cpu doesn''t save ss/rsp. 

Following trail from entry.S to show_registers(), I don''t see where
regs->rsp is loaded, yet show_registers() displays it happily.
show_stack() uses it. 

This also means that regs->rsp is actually going
to prev frame where orig hyp function was executing.

thanks,
Mukesh

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>>> Mukesh Rathor <mukesh.rathor@oracle.com> 24.02.10 04:39
>>>
>When a cpu is in hyp code and int/exception comes in, how/where is rsp 
>saved? According to intel manual if there''s no ring transition,
then
>the cpu doesn''t save ss/rsp. 
As you''re apparently talking about x86-64, you probably simply read
the wrong (32-bit) part of the manual. On 64-bits, ss:rsp are always
getting saved, no matter whether there''s a ring transition.

Jan


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On Wed, 24 Feb 2010 08:35:31 +0000
"Jan Beulich" <JBeulich@novell.com> wrote:
> >>> Mukesh Rathor <mukesh.rathor@oracle.com> 24.02.10 04:39
>>>
> >When a cpu is in hyp code and int/exception comes in, how/where is
> >rsp saved? According to intel manual if there''s no ring
transition,
> >then the cpu doesn''t save ss/rsp. 
> 
> As you''re apparently talking about x86-64, you probably simply
read
> the wrong (32-bit) part of the manual. On 64-bits, ss:rsp are always
> getting saved, no matter whether there''s a ring transition.
> 
You are right, few pages later, it talks about 64. Usually, they''ll say
something about things being different on 64bit. Anyways. I''ll email
intel
docs to fix it...

thanks,
Mukesh



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