changeset 1136:1d81002643e4

bitkeeper revision 1.758 (404306e9Uinl8Dzbmn07xevVeLqFRQ)

Add set_gdt description.
date Mon Mar 01 09:48:25 2004 +0000 (2004-03-01)
parents ca5de6ca0355
children 4d18dbf45e16
files docs/interface.tex
line diff
     1.1 --- a/docs/interface.tex	Sun Feb 29 17:45:39 2004 +0000
     1.2 +++ b/docs/interface.tex	Mon Mar 01 09:48:25 2004 +0000
     1.3 @@ -219,8 +219,27 @@ charge of performing page table updates 
     1.4  neccessary to prevent domains from adding arbitrary mappings to their page
     1.5  tables or introducing mappings to other's page tables.
     1.7 +\section{Segment Descriptor Tables}
     1.9 +On boot a guest is supplied with a default GDT, which is {\em not}
    1.10 +taken from its own memory allocation. If the guest wishes to use other
    1.11 +than the default `flat' ring-1 and ring-3 segments that this default
    1.12 +table provides, it must register a custom GDT and/or LDT with Xen,
    1.13 +allocated from its own memory.
    1.15 +int {\bf set\_gdt}(unsigned long *{\em frame\_list}, int {\em entries})
    1.16 +
    1.17 +{\em frame\_list}: An array of up to 16 page frames within which the GDT
    1.18 +resides. Any frame registered as a GDT frame may only be mapped
    1.19 +read-only within the guest's address space (e.g., no writeable
    1.20 +mappings, no use as a page-table page, and so on).
    1.21 +
    1.22 +{\em entries}: The number of descriptor-entry slots in the GDT. Note that
    1.23 +the table must be large enough to contain Xen's reserved entries; thus
    1.24 +we must have '{\em entries $>$ LAST\_RESERVED\_GDT\_ENTRY}'. Note also that,
    1.25 +after registering the GDT, slots {\em FIRST\_} through
    1.26 +{\em LAST\_RESERVED\_GDT\_ENTRY} are no longer usable by the guest and may be
    1.27 +overwritten by Xen.
    1.29  \section{Pseudo-Physical Memory}
    1.30  The usual problem of external fragmentation means that a domain is unlikely to