Xen devel - Dec 2007 - What''s allocated on head 1M region of domU?

Hi all.

I''m now try to read and write puseud physical memory of domU from Dom0
with xenaccess(this is using libxc).
#http://xenaccess.sourceforge.net/

With xenaccess, I''m succeeded read and writing almost of the memory.
But
It fail when I try to access head 1M region and some bit regions.
To be precise, xc_map_foreign_range() of libxc returns error code.
** <javascript:goWordLink("to")>

What''s allocated on head 1M region of domU?
#and , Can I get a document about memory allocation of dom0 and DomU
somewhere?

regards.

****************************************
HPCS lab
4th grade student of Colledge of Information Science, University of Tsukuba

Ryo Kanbayashi


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http://lists.xensource.com/xen-devel

> I''m now try to read and write puseud physical memory of domU from
Dom0
> with xenaccess(this is using libxc).
> #http://xenaccess.sourceforge.net/
Ah, cool.  I''d not heard much about XenAccess for a while, but I see
they''re
still progressing nicely - cool.
> With xenaccess, I''m succeeded read and writing almost of the
memory. But
> It fail when I try to access head 1M region and some bit regions.
> To be precise, xc_map_foreign_range() of libxc returns error code.
> ** <javascript:goWordLink("to")>
What error code do you get?  Are you trying to map the first meg all at once 
and it''s failing, or does it fail if you map any page in the first meg?
What
exactly is the call that''s failing?

I guess if you were trying to map the guest''s shared_info page then you
might
be disallowed...?
> What''s allocated on head 1M region of domU?
> #and , Can I get a document about memory allocation of dom0 and DomU
> somewhere?
See the comments starting around line 476 of xen/include/public/xen.h, which 
describes the start of day memory layout and defines some of the structures 
involved.  This will not be the same once the guest is up and running because 
the guest will allocate its own full pagetables and make its own decisions 
about where it wants to put stuff.  However, it''ll at least give you
some
clues about how the guest is built initially...  I hope this helps you some.

Cheers,
Mark



-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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Mark Williamson wrote:
>> I''m now try to read and write puseud physical memory of domU
from Dom0
>> with xenaccess(this is using libxc).
>> #http://xenaccess.sourceforge.net/
>>     
>
> Ah, cool.  I''d not heard much about XenAccess for a while, but I
see they''re
> still progressing nicely - cool.
>
>   
:-)
>> With xenaccess, I''m succeeded read and writing almost of the
memory. But
>> It fail when I try to access head 1M region and some bit regions.
>> To be precise, xc_map_foreign_range() of libxc returns error code.
>> ** <javascript:goWordLink("to")>
>>     
>
> What error code do you get?  Are you trying to map the first meg all at
once
> and it''s failing, or does it fail if you map any page in the first
meg?  What
> exactly is the call that''s failing?
>
> I guess if you were trying to map the guest''s shared_info page
then you might
> be disallowed...?
>
>   
I try to map no all at once.
I''ve figured out that top xen kernel is sitting on top 1M region :-|

thanks Mark.
>> What''s allocated on head 1M region of domU?
>> #and , Can I get a document about memory allocation of dom0 and DomU
>> somewhere?
>>     
>
> See the comments starting around line 476 of xen/include/public/xen.h,
which
> describes the start of day memory layout and defines some of the structures
> involved.  This will not be the same once the guest is up and running
because
> the guest will allocate its own full pagetables and make its own decisions 
> about where it wants to put stuff.  However, it''ll at least give
you some
> clues about how the guest is built initially...  I hope this helps you
some.
>
>   
I read the parts you suggested to me.
It helps me great :-)



regards.

****************************************
HPCS lab
4th grade student of Colledge of Information Science, University of Tsukuba

Ryo Kanbayashi


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

> > What error code do you get?  Are you trying to map the first meg all
at
> > once and it''s failing, or does it fail if you map any page in
the first
> > meg?  What exactly is the call that''s failing?
> >
> > I guess if you were trying to map the guest''s shared_info
page then you
> > might be disallowed...?
>
> I try to map no all at once.
> I''ve figured out that top xen kernel is sitting on top 1M region
:-|
Xen takes the top 64MB or a guest''s virtual address space.  But I
thought you
were trying to map the other end?
> > See the comments starting around line 476 of xen/include/public/xen.h,
> > which describes the start of day memory layout and defines some of the
> > structures involved.  This will not be the same once the guest is up
and
> > running because the guest will allocate its own full pagetables and
make
> > its own decisions about where it wants to put stuff.  However,
it''ll at
> > least give you some clues about how the guest is built initially...  I
> > hope this helps you some.
>
> I read the parts you suggested to me.
> It helps me great :-)
Good - those comments are some of the most useful anywhere in the codebase ;-)

Cheers,
Mark


-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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