RE: [Xen-devel] start of day mem layout

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> I am working on updating the mini-os to work on XEN 2.0. I am
> currently working on the memory management part of mini-os. I am
> trying to undestand the start of day memory layout that the guest
> domain (mini-os) gets from XEN when it 1st boots up. From what I
> undestand, 4 MB of memory are already mapped and virtual memory
> from 0xC000_0000 to 0xC040_0000 (4MB) are accessible. XEN already
> allocates a pgd and ONE page table for this 4MB vritual memory
> mapping.
 
A worthy effort, thanks for doing this.

I can't remember this stuff off-hand, but hopefully someone who's done a
port recently will speak up.

Ian


> I am booting mini-os with 16 MB of memory and these are the
> information I get:
> 
> shared_info                0xc0001000
> pfn_to_mfn                 0xc0010000
> Page Global Directory      0xc0014000
> Page Table                 0xc0015000
> start_info                 0xc0016000
> 
> Also, I think my kernel image contains some symbols such as _text,
> _etext, _edata, _end. 
> 
>  _text                     0xc0000000
> _etext                     0xc0007c04
> _edata                     0xc000d2c0
> _end                       0x819
> 
> I try to draw the virtual mem layout below. Sorry if it does not
> appear correctly because of different fonts.
> 
>                _edata             start_info
>                c000d2c0             c0016000
>   shared_info    |            PGD    |
>    c0001000      |         c0014000  |
>        |         |             |     | 
>   ------------------------------------------
>   |    |    |    |    |        |  |  |
>   |    |    |    |    |        |  |  |
>   |    |    |    |    |        |  |  |
>   ------------------------------------------
>   |         |         |           |
>   c0000000  |       c0010000    c0015000  
>   _text     |      pfn_to_mfn      PT
>             |
>           _etext         
>           c0007c04
> 
> I have a few questions. If someone could give some feedback that
> would be very appreciated.
> 
> I am not sure if those symbols _text, _etext, _edata and _end are
> meaningful or not, but is it correct to have the shared_info in the
> middle of my kernel image between _text and _etext ?
> 
> The default control ring between domain0 and a guest OS is found
> at shared_info + 2048 offset, is that still valid ?
> 
> Is there anything important after the start_info structure ?
> Is address starting at c0016000 + sizeof(start_info) available
> to use ?  
> 
> Also my _end symbol is found at address 0x819, so I don't quite
> udnestand that. Maybe something wrong I am doing in the linking
> process of my kernel image.
> 
> Thanks
> Richard
> 
> 
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