K 10
svn:author
V 8
cperciva
K 8
svn:date
V 27
2010-12-31T17:41:14.419842Z
K 7
svn:log
V 566
Make i386_set_ldt work on i386/XEN, step 4/5.

Use xen_update_descriptor to update the LDT rather than bcopy.  Under Xen,
pages used for holding LDTs must be read-only, so we can't make the change
ourselves.

Ths obvious alternative of "remap the page read-write, make the change, then
map it read-only again" doesn't work since Xen won't allow an LDT page to be
remapped as R/W.  An arguably better solution is used by NetBSD: They don't
modify LDTs in-place at all, but instead copy the entire LDT, modify the new
version, then atomically swap.

MFC after:	3 days

END