are there any hidden domains inside Xen when it is running?

are there any hidden domains inside Xen when it is running?

[Haifeng Fang]

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hi, all:

i have programmed a little tool which can dump some information of key data-struct inside xen.
with the tool, i obtained some data related to "frame_table" as follows:

page_offset, page_number, count_info, is_allocated, reference, inuse_domain_id, free_list_order
    502636KB,     125659,   80000002, allocated,          2,          1,          0
    516092KB,     129023,   80000002, allocated,          2,          0,          0
    516096KB,     129024,   80000001, allocated,          1,      32754,          0
    523248KB,     130812,   80000003, allocated,          3,      32753,          0

in my testing, i have brought up two domains, i.e. domain0(0), domainU(1). But from the list above, there are another two domains, who are they?

thanks in advance.
2008-06-04 



Haifeng Fang 

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Re: are there any hidden domains inside Xen when it is running?

[Ian Campbell]

On Wed, 2008-06-04 at 12:08 +0800, Haifeng Fang wrote:
> hi, all:
>  
> i have programmed a little tool which can dump some information of key
> data-struct inside xen.
> with the tool, i obtained some data related to "frame_table" as
> follows:
>  
> page_offset, page_number, count_info, is_allocated, reference, inuse_domain_id, free_list_order
> 
>     502636KB,     125659,   80000002, allocated,          2,          1,          0
>     516092KB,     129023,   80000002, allocated,          2,          0,          0
>     516096KB,     129024,   80000001, allocated,          1,      32754,          0
>     523248KB,     130812,   80000003, allocated,          3,      32753,          0
>  
> in my testing, i have brought up two domains, i.e. domain0(0),
> domainU(1). But from the list above, there are another two domains,
> who are they?

They are DOMID_XEN and DOMID_IO. From xen/include/public/xen.h:
        /*
         * DOMID_IO is used to restrict page-table updates to mapping I/O memory.
         * Although no Foreign Domain need be specified to map I/O pages, DOMID_IO
         * is useful to ensure that no mappings to the OS's own heap are accidentally
         * installed. (e.g., in Linux this could cause havoc as reference counts
         * aren't adjusted on the I/O-mapping code path).
         * This only makes sense in MMUEXT_SET_FOREIGNDOM, but in that context can
         * be specified by any calling domain.
         */
        #define DOMID_IO   (0x7FF1U)
        
        /*
         * DOMID_XEN is used to allow privileged domains to map restricted parts of
         * Xen's heap space (e.g., the machine_to_phys table).
         * This only makes sense in MMUEXT_SET_FOREIGNDOM, and is only permitted if
         * the caller is privileged.
         */
        #define DOMID_XEN  (0x7FF2U)

Ian.

>