Xen devel - Jun 2006 - How to map HVM guest virtual address to MMIO space?

I''m writing some code to test my new x86_emulate_memop() function in
QEMU, and I''m "stuck"... I want to map the VGA memory (one
page at
0xB8000 in guest-physical memory) to some completely different virtual
address (say 0x4000000 for arguments sake). I''ve got a paging-enabled,
with a 1:1 mapping (for easy of coding), and it works fine to run the
code (now that I''ve figured out the correct values to shift the virtual
address when setting the page-table up). But when I try to map the VGA
memory, it doesn''t seem to behave like I want - it''s not
recognised by
mmio_space(). How should I do this? 

As far as I understand, just setting the correct entries in the page
table to point to 0xB8000 should do it, right?

[It''s still quite possible that there''s more bugs in my code,
I''m just
asking this in case I''ve missed something (else)...]

--
Mats



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> -----Original Message-----
> From: Petersson, Mats 
> Sent: 28 June 2006 14:33
> To: xen-devel@lists.xensource.com
> Subject: How to map HVM guest virtual address to MMIO space?
> 
> I''m writing some code to test my new x86_emulate_memop() 
> function in QEMU, and I''m "stuck"... I want to map the
VGA
> memory (one page at 0xB8000 in guest-physical memory) to some 
> completely different virtual address (say 0x4000000 for 
> arguments sake). I''ve got a paging-enabled, with a 1:1 
> mapping (for easy of coding), and it works fine to run the 
> code (now that I''ve figured out the correct values to shift 
> the virtual address when setting the page-table up). But when 
> I try to map the VGA memory, it doesn''t seem to behave like I 
> want - it''s not recognised by mmio_space(). How should I do this? 
> 
> As far as I understand, just setting the correct entries in 
> the page table to point to 0xB8000 should do it, right?
> 
> [It''s still quite possible that there''s more bugs in my
code,
> I''m just asking this in case I''ve missed something
(else)...]
In fact, I was trying to use the same PTE as something else, and ended
up not doing the right thing, so it was a bug in my code.

And to answer my own question, you just make the virtual address point
to the VGA memory, and all works just as you''d expect. It just
doesn''t
work when the page-tables aren''t set up correctly!
Doh!
> 
> --
> Mats


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